Lake Victoria is the second largest freshwater lake in the world that was once a biodiversity hotspot hosting over 500 endemic haplochromine cichlids that were later decimated by exotic introductions and anthropogenically driven environmental and ecological changes. The environmental and ecological changes in the lake over the years have been attributed to overfishing, eutrophication, introduction of exotic species, pollution and possibly climate change. The lake's capture fishery, which is the main economic activity directly and indirectly supporting over 40 million people, has continued to decline after experiencing a boom between the 1970s and 1990s following the introduction of Nile Perch (Lates niloticus) and Nile Tilapia (Oreochromis niloticus). In order to augment capture fisheries from the lake, cage culture was introduced in 2005, but its sustainability and influence on the ecology of the lake are not well understood. In this review, we examine the genesis of degradation of Lake Victoria and assess the role of cage culture as both a solution to the current situation and a cause for concern for the ecology of the lake. To compile this review, we utilized data in the grey and published literature. Studies show that the degradation of the lake can be traced back to the 1930s when the trophic status and ecology of the lake started showing signs of anthropogenic influence. The Nile Perch was introduced in early 1960s to replenish the fishery but its ecological impacts were felt in 1970s and 1980s when the native haplochromine species started to disappear from catches. Progressively, the ecological changes and management concerns in the lake have become a complex mix of exotic species introductions, eutrophication, and overfishing. In this mix of persistent ecological changes, the once thriving capture fisheries revolving around the two exotic species (L. niloticus and O. niloticus) have significantly declined threatening the livelihoods of millions of people directly and indirectly involved in the fisheries. These declines necessitated the introduction of cage culture in 2005 to fill the increasing demand for fish from the lake. Ever since, cage numbers have increased tremendously (>6 000 by 2020) and is now operated by over 60 different firms which are owned either individually or by groups. Over 70% of the cages have been installed in shallow areas within the Winam Gulf which goes against the guidelines on cage installation and operation; regulations on cage farming were introduced after the activity had gained momentum in the lake. Limnological data in areas of the lake that have been stocked with cages has shown evidence of negative effects on water quality. This decline in water quality can be attributed to remnant feeds used in cages, of which 50% are the sinking types, and wastes from fish excretion and egestion. Although data are limited, the potential influence of cage farming on the already altered ecology and environment of Lake Victoria needs to be recognized and investigated. This study recommends studies targeting operations of cages in the lake, including a comprehensive environmental audit to inform their sustainability and relevant policy.

The production of phytoplankton (algal) toxins and their control is of concern because of the need to reduce their negative impacts on water quality and facilitate effective management of algal blooms. The present study was conducted between September 2017 to May 2018, focusing on Kisumu Bay in the Kenyan portion of Lake Victoria, in order to establish the magnitude of potential impacts on phytoplankton composition and microcystin following a prolonged presence of water hyacinth coverage between 2013 and 2018 within the gulf, with an estimated coverage range varying between 644 and 1224 ha. Triplicate samples of physico-chemical parameters, nutrients, phytoplankton, chlorophyll-a and algal toxins (N = 88) were collected at eleven sampling sites to determine their spatio-temporal variability. The main identified algal taxa comprised Cyanophyceae, Bacillariophyceae, Chlorophyceae, Euglenophyceae, Zygnematophyceae and Dinophyceae. The most dominant algal species were Microcystis aeruginosa (25%), Merismopedia spp. (23%) and Anabaena flos-aquae (16%).Enzyme-linked immunosorbent assay (ELISA) technique was used to determine microcystin (MC) toxins in the water. Mean MC-LR and MC-YR concentrations were significantly correlated (R 2 = 0.972), exceeding WHO standards at three sampling sites (Coca Cola, 2.84 ± 4.76; Kisumu pier, 1.78 ± 1.87; Midpoint, 1.44 ± 2.71 μg/L MC-LR). There were significant temporal variations (p < .05) in the SRP, TN, NO 3 -N, NO 2 -N, NH 4 -N, SiO 2 -Si, MC-LR, MC-YR, dissolved oxygen (DO), total dissolved and suspended solids (TDS; TSS), turbidity, electrical conductivity, Secchi depth, temperature and pH levels. The water depth, TP and DO also vary spatially. The nitrogen to phosphorus concentration ratios differed from the expected N:P ratio of 16:1, indicating a highly eutrophic status. The disproportionate ratio of total phosphorus and total nitrogen in the bay may be responsible for the enhanced cyanobacterial blooms it exhibits. The results of the present study provide useful information and data for formulating regulations for water quality management.

Persistent organochlorine residues in the environment are a threat to ecological health of aquatic organisms and pose a health risk to both animals and human consumers. Organochlorine pesticides were determined in water and sediments collected during wet and dry season from selected riverine and earthen fish pond sites in high altitude catchment areas within Kuja River (Kenya) between August 2016–May, 2017. Analysis of DDT and metabolites, Hexachlorocyclohexanes (HCHs) isomers and cyclodienes using a gas chromatograph (GC), and electron capture detector (ECD), confirmed using GC - Mass Spectrometry (MS). Mean (± Standard error) results of DDTs, cyclodienes and HCHs in pond waters were:- below detection level (BDL) to 0.27±0.03µg/L, BDL to 0.11±0.00µg/L, and 4.39±1.01µg/L respectively; and BDL to 0.23±0.01µg/L, 1.20±0.005µg/L, and 1.71±0.02µg/L in river water respectively. Sediment mean OCPs contents were significantly (p<0.05) higher for Dieldrin (3.043±0.43µg/kg), Endrin (2.56±0.460µg/kg), Heptachlor (3.61±0.02µg/kg) DDT (2.97±1.32µg/kg), Endosulfan (6.31.27±1.051µg/kg), Methoxychlor (2.15±1.641µg/kg) and Lindane (2.96±1.32µg/kg), respectively. A longitudinal spatial distribution pattern was noted for both water and sediment OCPs contents, demonstrating that cyclodienes are predominant contaminants in point and non-point sources in water courses. The study recommends continuous monitoring of OCPs in upstream catchment areas for informed management and policy decisions on pesticide use. Keywords: Kuja-Migori River; Organic contaminants; Organochlorine Pesticide.