Water Hyacinth Re-invades Lake Victoria

From NASA’s Earth Observatory, images showing the speed with which the rapidly spreading S American water hyacinth has reinvaded Lake Victoria. Water hyacinth was introduced to Africa over a century ago, but it did not become a problem in Lake Victoria until the early 1990s. It covered substantial areas of the coastline, particularly in Uganda, blocking waterways, disrupting hydropower, and decreasing the profitability of fishing. Hyacinth also provided refugia for some species from the introduced Nile Perch. It largely disappeared from the Lake in the late 90s, perhaps, but not clearly, due to the introduction of a weevil used for biological control. It experienced a resurgence in the early 2000s. Now following a wet year, which increased nutrient runoff into the lake, water hyancinth has returned.

water hyacinth

These images show the Winam Gulf, in the northeast corner of Lake Victoria in Kenya. The gulf was the most severely affected region during the first hyacinth outbreak in 1998, with as much as 17,231 hectares (67 square miles) of the plant growing on its surface. By 2000, the area covered by water hyacinth was down to about 500 hectares (2 square miles), and in December 2005, when the right image was taken, the lake appeared to be clear. In November and December 2006, however, unusually heavy rains flooded the rivers that feed into the Winam Gulf. The rain and floods raised water levels on the lake and swept agricultural run-off and nutrient-rich sediment into the water. As a result, the Winam Gulf was brown when the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite took the top left photo-like image on December 18, 2006. Vegetation around the lake was dramatically greener due to the rains.

The influx of fertilizer and sediments not only turned the water brown, but it also fed a fresh outbreak of water hyacinth. Bright green plants cover much of the Winam Gulf in the top left image. Though other plants such as algae may be contributing, water hyacinth is almost certainly one component of the soupy mass. As the photo shows, water hyacinth was growing along the shoreline, particularly in Kisumu Bay and Nyakach Bay. A comparison between December 2005 and December 2006 shows that Kisumu Bay was entirely covered by water hyacinth in 2006, and the shoreline of Nyakach Bay also appeared to change shape as the plant grew out from the shore.

The photo was taken on December 17, 2006, looking north across Kisumu Bay. The photographer stands on the shoreline and should be looking out over water, but only a field of green water hyacinth can be seen. The photo illustrates the problems the plant poses to the lake. The mat of vegetation is so thick that fishermen cannot launch their boats or bring fish to market on the shore. Sunlight does not filter through the plants, so native plants in the lake don’t get the light they need. The die-off of native plants affects fish and other aquatic animals. Water hyacinth clogs irrigation canals and pipes used to draw water from the lake for cities and villages on its shore. The plants impede water flow, creating abundant habitat for disease-carrying insects like mosquitoes. Water hyacinth can also sap oxygen from the water until it creates a ”dead zone” where plants and animals can no longer survive. Typically, only aggressive measures can control the fast-growing plant.

18 thoughts on “Water Hyacinth Re-invades Lake Victoria”

  1. This is big, unwelcome, but not altogether surpising news. It is probably important to note that the weevil’s role in the ca. 2000 collapse was limited. Satellite imagery in our paper ( http://edcintl.cr.usgs.gov/lakespecialfeature.html ) clearly showed declines in most parts of the lake either prior to, concurrent with, or immediately following (probably too soon for the weevils to have been able to do their thing) the introduction of the weevils.

    I can’t offer more than speculation about what was more repsonsible for that decline, but heavy rains and associated wind/wave battering are a strong possibility.

    Hopefully this round of water hyacinth will pass quickly and we are able learn a bit more this time.

  2. The dynamics of water hyacinth versus weevil control makes an interesting debate. Its true that the weevils played a major part in the decline of water hyacinth biomass on Lake Victoria in the late 1990’s to 2000. As Biocontrol scientist who was involved in the thick of it all, I can fairly confidently say that the reinversion being seen is a normal sigmoid trend often seen in many biocontrol programmes.

    When me and my team first released weevils in 1995, an estimated 12,000ha covered L. Victoria, however, the weevil population literally exploded and by 1998 the weed mats were teaming with over 15 weevils/plant and hence the browning and drying up of the weed mats. By 2000 virtually all the mats were eaten up so with no food readily available, most of the bugs perished. Therefore seeds left behind by the dying water hyacinth (under ecological pressure water hyacinth often rapidly flowers to deposit seeds for the next generation), slowly germinated and flourished under a condition devoid of the bugs but rich in nutrients from the decomposing water hyacinth mats.

    The result is the current apparent blooming of the weed. The few weevils that survived have slowly been building up in population. During My last visit to one of the bays (Thruston Bay) last weekend, I found the same process of weevil population explosion that occurred in the 1990’s at work again. I sampled 40 plants and was amazed that the weevil population is at present 10 weevils/plant and the infested water hyacinth plants are already clearly showing the typical stunting and drying up. In my view and experience, I can confidently predict that sooner that later dry mats teaming with millions of weevils will soon be seen floating in the Lake. By the way, in the late 1990’s, the drying dead mats infested with millions of the bugs was interprated as a result of night spraying of herbicides.

    Hopefully, this time around interested parties will have the opportunity of visiting L. Victoria to witness. I must add that I had the opportunity to witness the success of biocontrol of water hyacinth on L. Victoria with world leaders in this filed like Dr Peter Neuenscwander (IITA – Benin) and Mic Julien (CSIRO – Australia). Thomas Moorhouse of Clean Lakes was an active player in the success.

  3. James, thanks for the explanation of what is currently going on and presenting your ideas about what is going on. It would be great to hear more about what is going on with Lake Victoria.

  4. Can the water from areas covered by the hyacinth be used for irrigating vegetables like onions or tomatoes.
    What effect will it have on crops?
    I notice that even cows now do not drink the water?

    please email me back on namoneko@yahoo.com


    The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp.
    John R.U. Wilson, Obinna Ajuonu, Ted D. Center, Martin P. Hill, Mic H. Julien, Francisca F. Katagira, Peter Neuenschwander, Stephen W. Njoka, James Ogwang, Rob H. Reeder and Thai Van


    There has been some debate recently about the cause of the decline of water hyacinth on Lake Victoria. While much of this evidence points to classical biological control as the major factor, the El Nio associated weather pattern of the last quarter of 1997 and the first half of 1998 has confused the issue. We argue first that the reductions in water hyacinth on Lake Victoria were ultimately caused by the widespread and significant damage to plants by Neochetina spp., although this process was increased by the stormy weather associated with the El Nio event; second that increased waves and current on Lake Victoria caused by El Nio redistributed water hyacinth plants around the lake; and third that a major lake-wide resurgence of water hyacinth plants on Lake Victoria has not occurred and will not occur unless the weevil populations are disrupted. We conclude that the population crash of water hyacinth on Lake Victoria would not have occurred in the absence of the weevils, but that it may have been hastened by stormy weather associated with the El Nio event.

    1. Introduction

    Water hyacinth was first reported on Lake Victoria in 1989 (Twongo, 1991), and quickly spread around the lake margins. At the peak of the infestation in the late 1990s, data from Albright et al. (2004) suggest that tens of thousands of hectares of the water surface were covered in plants. This infestation hampered transport links, reduced levels of fishing, and posed a threat to the biodiversity of the lake, including its unique fauna of cichlids (Seehausen et al., 1997). To control the weed, classical biological control agents (Neochetina bruchi (Hustache) and Neochetina eichhorniae (Warner) (Coleoptera: Curculionidae) were imported to the Great Lakes Region, and from 1995 onwards they were released onto different parts of the lake. During 1997/1998, there was also an El Nio weather pattern that caused stormy and wet weather in the region. Around the same time, water hyacinth populations started declining on the lake. This decline has continued and there are no reputable reports of any major resurgence of the weed.
    In this paper we want to address a recent article in Aquatic Botany by Williams et al. (2005) which states that Weevils alone were probably not responsible for the rapid reduction in weed biomass, but that the wet and cloudy weather of 1997/1998 almost certainly played a major part by accelerating their decline due to extremely low light availability . They also warn that in the absence of El Nio effects, weevil populations will be unstable and that the return of water hyacinth proliferation within Lake Victoria may therefore be just a matter of time. We reanalyze the data of Williams et al. (2005) and, to see whether light had indeed been critically low, we establish a time series of the dynamics of water hyacinth on Lake Victoria and present observations on water hyacinth population dynamics from around the world. We arrive at different conclusions, namely that water hyacinth was controlled by weevils and that the probability of water hyacinth resurgence has been overplayed. In so doing, we reiterate arguments made by Ogwang and Molo (2004), but in the light of new supporting evidence.

    2. Methods

    A recent study used satellite images of Lake Victoria to estimate the coverage of water hyacinth on the Tanzanian, Ugandan and Kenyan (Winam Gulf) sides of the lake (Figs. 4, 6, and 7 in Albright et al.,
    2004). In our study, each data-set was linearly interpolated between sample dates, and the resulting trends were summed to give a picture of how lake-wide water hyacinth populations changed over time (Fig. 1). The pattern produced corresponded well with the lake-wide data presented (Fig. 1 in Albright
    et al., 2004), but included more data as our approach was not restricted to dates where the whole of the lake was clear from cloud cover.
    In Fig. 1, water hyacinth populations declined just after the El Nio event (although the sustained reduction in plant populations started about a year later). To test whether low light levels per se could have restricted water hyacinth growth, Williams et al. (2005) measured how CO2 uptake changed with light levels (Fig. 2 in Williams et al., 2005), and separately how plant growth varies with CO2 uptake rate when photosynthetic active radiation (PAR) was >2000 ?E m?2 s?1 (Fig. 3 in Williams et al., 2005).
    In extrapolating from light levels to plant growth, Williams et al. (2005) imply a relationship between water hyacinth growth (in terms of biomass accumulation) and instantaneous light levels. Given the parameter estimates of Table 1 in Williams et al. (2005), we established this relationship and evaluated its consequences.

    2. Results and discussion

    Albright et al. (2004) provided the first clear data on lake-wide water hyacinth abundance, and it was clear from our redrawing that the lake-wide level of water hyacinth cover increased rapidly from 1995 to 1998 (Fig. 1). There appeared to be a decline during the first half of 1998 co-inciding with an El Nio event, but in the latter half of 1998 the water hyacinth population appeared to be again climbing rapidly.
    The major turning point appears to have come in early 1999 and by the start of 2000 the population had declined and has maintained a more stable level of under 1000 ha. Given that weevils were first introduced late in 1995, it took at most 4 years for control to be effective. This time-frame is consistent with observations from other countries (Center, 1994, Julien et al., 1999 and Center et al., 2002). There were some manual control measures and a few mechanical harvesters, but there were no large-scale herbicide spraying programs on Lake Victoria. Therefore, classical biological control represents the only control method that was implemented across the whole of the lake and the most likely hypothesis to explain the dramatic reduction in water hyacinth populations. While biological control of water hyacinth by Neochetina spp. has been less effective in some sub-tropical regions (Hill and Olckers, 2000), the weevils have lead to clear reductions in plant density in West Africa (Ajuonu et al., 2003); Papua New Guinea (Julien and Orapa, 1999); and in warmer areas of South Africa (Hill and Olckers, 2000). In each case, biological control agents were the only control measure in place. Neochetina larvae tunnel the petioles and the root-stock, thereby allowing bacteria and secondary fungi to enter the plant and cause severe damage. Direct destruction of aerenchymous tissue and the flooding of old larval tunnels will reduce plant buoyancy. Consequently, one of the characteristics of control by Neochetina weevils is that water hyacinth mats become water-logged and sit lower in the water. As plant destruction increases the mats sink to the bottom of the water-body.
    By increasing wind and wave action, the El Nio event may have been a major stress to plants. If plants are already badly damaged due to insect feeding and secondary damage, it is clear that wave action has a much greater impact by breaking up mats and submerging damaged plants.
    It is expected that increased surface currents and wave action reinforced by El Nio, would also move mats around the lake leading to some contradictory conclusions and explaining local reports of resurgences. Indeed, Albright et al. (2004) suggest this may explain the reduction in water hyacinth on the Tanzanian side in 1998 and the increase in the relatively sheltered Winam Gulf, which would have received plants blown in by the prevailing winds. Reports of a resurgence [that] may be re-starting date back to 2000, and they understandably generated concerns. However, studies showed that the young healthy rapidly growing plants that had appeared were the result of the germination of seeds which had been deposited in the sediment. Their germination had been stimulated by the collapse of large mats, allowing easier light penetration of the water. Seedling growth may have been enhanced by high levels of nitrates and phosphates in the water due to runoff from agriculture and urban deposition that was no longer taken up by the large water hyacinth mats, and also to the release of nutrients from those mats decaying on the bottom of the lake. In contrast, the weevil populations in the area were very low, presumably because eggs, larvae, and pupae sank with the mats and drowned, while adults would have dispersed as the plant quality of the old mat declined. Therefore, the new growth was able to proliferate in the absence of weevils. The weevils, in due course, dispersed naturally back onto these fringes of plants in the western arm of the lake. A survey conducted in October 2000, recorded an average of three adult weevils per plant at one site, indicating that the weevils were already invading the new growth (Ogwang, 2001).
    Williams et al. (2005) state that weevil populations although present are likely unstable and suggest that this may lead to a resurgence in water hyacinth populations within Lake Victoria. This statement is unsubstantiated. One of the basic tenets of classical biological control of weeds is that it is sustainable through population regulation (DeBach, 1964). Whilst insect populations change in response to variations in the densities of the host plant and environmental conditions, this does not mean that control fails to be exerted. Given the reduction in buoyancy caused by weevil feeding and the strong wave action of the lake, a large mat cannot develop in future unless the herbivore pressure is removed.
    The dynamic nature of water hyacinth on large water-bodies means that plants may temporarily escape this herbivore pressure. Variations in nutrient quality around the lake will lead to variation in dynamics, and these effects have been seen in other systems. However, as agents become established throughout the head-waters, both the quantity of material coming into the lake should be reduced (this was estimated at around 0.75 ha day?1 during 1999 (Moorhouse et al., 2000)); and any material coming into the lake is likely to be infested by weevils. Only thanks to a lake wide standardized survey of the type presented in Albright et al. (2004), has the pattern become apparent, and it is clear from continuing observations that the massive infestations of the 1990s have not returned. Lake Victoria is the largest single water body for water hyacinth biological control. There is no a priori reason to suppose that Lake Victoria will be an inherently unstable system, as substantial sustained control within 35 years has been a feature of water hyacinth control in the tropics even on large water bodies (Julien et al., 1999) (e.g. 3 years after releasing weevils an infestation of 500 ha on the 2500 ha Sanalona Dam in Mexico was reduced to 150 ha (Aguilar et al., 2003)). However, where plant and insect dynamics are disrupted by frost or foliar herbicides, weevil populations are slow to respond (Wilson et al., 2006), partly because the development of weevils takes at least 70 days. More work is required to establish whether nutrient inputs to the lake could result in a scenario where control in eutrophied bays is no longer satisfactory (either in terms of stability or average level). Continued monitoring of water hyacinth and water hyacinth weevil populations is therefore recommended.
    It seems highly unlikely that cloudy weather associated with the El Nio event of 19971998 can explain the massive reduction in water hyacinth of 19992000. As with many tropical locations, the cloud cover in West Africa and Papua New Guinea is often thick and persistent, but this did not prevent either water hyacinth from becoming a problem or the water hyacinth weevils from causing extensive damage to plants (Julien and Orapa, 1999 and Ajuonu et al., 2003). The data presented by Williams et al. (2005) does not provide a substantive link between low light levels on Lake Victoria and plant mortality. The weekly midday PAR on Lake Victoria varied 18004400 ?E m?2 s?1 between 1996 and
    2001 (Fig. 4 in Williams et al., 2005), light levels that would allow significant plant growth (depending largely on plant size and less on light levels, growth rates based on the proposed relationship would range 0.030.10 g g?1 day?1). However, the effect of changes in field light levels on water hyacinth population dynamics remains an active research question. Plants certainly survive and prosper in very shady back-waters that never receive direct sun-light, but clearly plants will also die if light is low enough for long enough (Brochier et al., 1985). We suggest that measurements of photosynthetic efficiencies should be made in situ, e.g. by using various shade treatments on water hyacinth mats.
    Plants grown in small containers (e.g. Fig. 1 in Williams et al., 2005) suffer from an island or clothesline effect, where transpiration is much higher than normal (Allen et al., 1997). Plant size and nutrient status must also be considered as there is a strong robust linear correlation between growth rate and biomass density and between growth rate and nutrient conditions (Wilson et al., 2005).
    The effect of El Nio has confused the issue of water hyacinth control in Lake Victoria. Because of the mobility of mats and changing currents caused by El Nio, the quantity of water hyacinth at any one location was quite variable. However, the lake-wide picture is much clearer. While we agree wholeheartedly with Williams et al. (2005) in stressing the need to reduce nutrient inputs to tropical lakes there is little doubt that the devastating problems caused by water hyacinth would not have been alleviated without biological control agents. Given the rate at which the benefits from successful biological control programs scale with the size of the problem (DeGroote et al., 2003 and McConnachie
    et al., 2003), the continuing economic value of the classical biological control intervention on Lake Victoria is considerable.


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    O. Ajuonu, V. Schade, B. Veltman, K. Sedjro and P. Neuenschwander, 2003 Impact of the weevils Neochetina eichhorniae and N. bruchi (Coleoptera: Curculionidae) on water hyacinth, Eichhornia crassipes (Pontederiaceae) in Benin, West Africa, Afr. Entomol. 11 (2003), pp. 153162.

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    Society of Florida, vol. 56 (1997), pp. 110

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    T.D. Center, 1994 Biological control of weeds: water hyacinth and water lettuce. In: D. Rosen, F.D. Bennett and J.L. Capinera, Editors, Pest Management in the Subtropics: Biological Controla Florida Perspective, Intercept Publishing Company, Andover, UK (1994), pp. 481521 (Chapter 23).

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    H. DeGroote, O. Ajuonu, S. Attignon, R. Djessou and P. Neuenschwander, 2003 Economic impact of biological control of water hyacinth in Southern Benin, Ecol. Econ. 45 (2003), pp. 105117.

    M.P. Hill and T. Olckers, 2000 Biological control initiatives against water hyacinth in South Africa: constraining factors, success and new courses of action. In: M.H. Julien, T.D. Center and M.P. Hill, Editors, Second IOBC Global Working Group on the Biological and Integrated Control of
    Water Hyacinth ACIAR, Beijing, China (2000), pp. 3338.

    M.H. Julien, M.W. Griffiths and A.D. Wright, 1999 Biological control of water hyacinth, The Weevils Neochetina bruchi and N. eichhorniae: Biologies, Host Ranges, and Rearing Releasing and Monitoring Techniques for Biological Control of Eichhornia crassipes, Australian Centre for International Agricultural Research (ACIAR), Canberra (1999).

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    (Eichhornia crassipes) in Papua New Guinea by the weevils Neochetina bruchi and Neochetina eichhorniae (Coleoptera: Curculionidae). In: N.R. Spencer, Editor, Proceedings of the X International Symposium on Biological Control of Weeds Montana State University, Bozeman, MT, USA (1999), p.
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    J.A. Ogwang and R. Molo, 2004 Threat of water hyacinth resurgence after a successful biological control program, Biocontrol Sci. Technol. 14 (2004), pp. 623626.

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  6. I have read with much interest the story of resurgence in water hyacinth across Lake Victoria. I see that James Ogwang has posted a paper that he and several authors wrote in response to a paper that myself and others wrote. For completedness you can find both the original paper and moreover a peer reviewed response to the paper presented by James above at the following addresses. Please note that you can copy these addresses into your web browser but that the chain has to be complete and as a single line.

    http://freespace.virgin.net/ae.williams/New/2007 Williams et al – A
    quatic Botany – 87 – 94-96.pdf

    http://freespace.virgin.net/ae.williams/New/2005 Aquatic Botany – 81 – 300-314 Water hyacinth (Eichhornia crassipes) in Lake Victoria – why did it vanish so quickly and will it return .pdf

    Overall I believe that there are numerous interacting factors that have helped control WH so far but that it’s continued control is far from certain. Continued work that looks at control pathways and the extent of cover across Lake Victoria is essential.

  7. Just accidentally bumped into this site.
    Now that the debate on water hyacinth is back, albeit at a more milder fasion and with greater understanding, it is becoming increasingly necessary to allay the fears that the chosen method of control did not work, (probably looking at the resurgence, one would wrongfully believe that this is so). I remember looking at a paper done by by a Canadian Prof (I believe this should be Robert Hecky) and there was somewhat of a prediction that this resurgence was bound to take place.

    However, convincing people that this is a problem they will have to live with is not one of the easiest of tasks. Nobody likes bad news and even though quite a lot of such messages have been passed before it is as though communities keep forgetting about this fact and hence it appears as thogh more sensitization will be necessary. Anybody in Uganda and Tanzania and Rwanda too need to tell us exactl how reidents are dealing with this resurgence. Granted that from observation, Nyanza gulf may be experiencing more of the weed, are there real explanations (maybe wind patterns, the sheltered bays or is it to do with more cultivation upstream) for this situation? Maybe riparian communities of the Nyanza gulf are more affected?

    Do we also have a consistent water hyacinth surveillance and monitoring system in place? In other words, is there a consistent database containing details of the infestation of water hyacinth which researchers can rely on save for the occasional satellite images they may rely on for a preview of the situation on selected dates? Such consistent monitoring I believe can give us hints into which environmental conditions may act as predisposing factors to resurgence if they actally do.

  8. i am also working on waterhyacinth and want to know about bio control through insects and mycopathogens.

  9. i am a research scholar in botany department of allahabad university,India.i want to know life cycle of neochetina eicchorniae,which is a potent biocontrol agent of water hyacinth.tell me about types of larva and caterpillars harbouring on the same weed.

  10. I am currently working on a project in Kisumu Port and when I visited the site in December 2007, the port was heavily infested with water hyacinth. I would like to get access to data on how the coverage varies with winds, I have been told that the dense mat floats into and out of the port with the wind. Does anyone have pictorial evidence of this? The discussion on this forum does not seem to support this claim.

  11. Iam a post graguate student based in maseno university and working on possibilities of using water hyacinth as a by-product in manufacture of poultry feeds. I strongly believe that water hyacinth is a God send natural resource and hence people should attempt to use it and not declaring war on it. After all it cleans our heavily polluted lakes/rivers.

  12. I found this page while trying to get a little background on an interesting new project involving water hyacinths that Swahili Imports is working with in Kenya. Artisans near Lake Victoria are mashing the water hyacinth into a pulp, which they then turn into paper. They use the paper to craft animal sculptures, which they then export to gift shops around the world.

    While this project won’t wipe out a massive amount of the water hyacinth choking Lake Victoria, it is an interesting local response to the problem that helps generate much-needed shillings.

    We’re receiving our first shipment of these water hyacinth paper mache sculptures in September, and they’ll be posted on our website once they arrive.

  13. Tantrum. the most logicall thing that bothers me alot is how the weed came into the lake?

  14. Do you know?
    Biological control of WH was inagurated for the first time (after South Africa)in the Sudan. Natural enemies were released in collaboration with the Commonwelth Institute of Biological Control, and the University of Khartoum and the Ministry of Agriculture and Forestry (Plant Protection Directorate(PPD) in 1997-1998. Now waterhyacinth is no log considered as a national pest as it used to be considered. Now the Nile in Sudan is navigable as it used to be before the advent of WH. The Acacia nilotica and other trees and plants came back to stud the banks of the river after the days of 2-4D are over.

  15. Dear sir / Madam,

    I have recently pyblished a paper on water hyacinyh bilogical control by grass carp and weevil. It willb useful to all the concerned.
    “Integrated biological control of water hyacinths, Eichhornia
    crassipes by a novel combination of grass carp,
    Ctenopharyngodon idella (Valenciennes, 1844), and the
    weevil, Neochetina spp.*Chinese Journal of Oceanology and Limnology
    Vol. 29 No. 1, P. 162-166, 2011.
    DOI: 10.1007/s00343-011-0101-z

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