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Lake Victoria has experienced progressive eutrophication which has exacerbated the proliferation of cyanobacterial harmful algal blooms (cHABs). Fueled by anthropogenic nutrient loadings and climate change, these cHABs are increasing in distribution, duration, and frequency, particularly in areas such as the Winam Gulf. With limited resources and infrastructure, local communities have been left vulnerable as they rely on the lake for water for domestic use. Our study presents the results of a localized survey on how small-scale fishing communities perceive and respond to the threat of cHABs in the Winam Gulf of Lake Victoria, Kenya. We used a mixed-methods approach of quantitative and qualitative data-gathering techniques to elucidate the perceptions and consequences of cHABs in local communities. Our results demonstrate most (93.67%) respondents were aware of cHABs in the lake, but were not knowledgeable of cHAB threats to human and animal health. Respondents noted that fish catches decreased during cHABs, with this economic consequence serving as a primary concern of communities. Notably, respondents altered their use of lake water during perceived cHAB events and relied on other means of water treatment or alternative water sources. Overall, cHAB information was selfsourced or passed on from community elders, with no public mechanism for adequate cHAB risk communication. Lake Victoria serves as a critical resource to the Eastern African region and requires a concerted cHAB response effort. Therefore, we recommend the development of a public awareness program to reduce cHAB exposure in these at-risk communities. 

ABSTRACT The Winam Gulf in the Kenyan region of Lake Victoria experiences prolific, year-round cyanobacterial harmful algal blooms (cyanoHABs) which pose threats to human, livestock, and ecosystem health. To our knowledge, there is limited molecular research on the gulf’s cyanoHABs, and thus, the strategies employed for survival and proliferation by toxigenic cyanobacteria in this region remain largely unexplored. Here, we used metagenomics to analyze the Winam Gulf’s cyanobacterial composition, function, and biosynthetic potential.Dolichospermumwas the dominant bloom-forming cyanobacterium, co-occurring withMicrocystisat most sites.MicrocystisandPlanktothrixwere more abundant in shallow and turbid sites. Metagenome-assembled genomes (MAGs) ofDolichospermumharbored nitrogen fixation genes, suggesting diazotrophy as a potential mechanism supporting the proliferation ofDolichospermumin the nitrogen-limited gulf. Over 300 biosynthetic gene clusters (BGCs) putatively encoding the synthesis of toxins and other secondary metabolites were identified across the gulf, even at sites where there were no visible cyanoHAB events. Almost all BGCs identified had no known synthesis product, indicating a diverse and novel biosynthetic repertoire capable of synthesizing harmful or potentially therapeutic metabolites.MicrocystisMAGs containedmcygenes encoding the synthesis of hepatotoxic microcystins which are a concern for drinking water safety. These findings illustrate the spatial variation of bloom-forming cyanobacteria in the Winam Gulf and their available strategies to dominate different ecological niches. This study underscores the need for further use of genomic techniques to elucidate the dynamics and mitigate the potentially harmful effects of cyanoHABs and their associated toxins on human, environmental, and economic health. 

ABSTRACT We report 40 metagenomic libraries collected from the Winam Gulf of Lake Victoria during May–July of 2022–2023 and an additional eight opportunistic libraries from adjacent Lakes Simbi, Naivasha, and regional river systems. The sampling period captured cyanobacterial bloom events – shedding insight onto community composition and genomic potential.