Benard Mucholwa Simiyu talks about his PhD on water quality in Nyanza Gulf, Kenya

23. May 2022
Portrait Benard Mucholwa Simiyu
APPEAR scholar Benard Mucholwa Simiyu successfully completed his PhD live online from Technical University of Kenya on 15 February 2022. In this article, he provides insights on his PhD research on the influence of the main Lake Victoria on the water quality in Nyanza Gulf.

APPEAR scholar Benard Mucholwa Simiyu graduated as PhD student at the Research Department for Limnology, University of Innsbruck, Austria. His dissertation was supervised by Prof. Rainer Kurmayer and Prof. Eugen Rott from the University of Innsbruck, Austria. The study titles "The effects of hydrological changes on the spatial phytoplankton composition and cyanotoxin concentrations in Nyanza Gulf, Lake Victoria, Kenya". It focuses on Nyanza Gulf (Winam or Kavirondo), which is one of the largest, shallowest and semi-enclosed waters of Lake Victoria basin with an area of 1400 km2 and a mean depth of 5m.

In the past few decades, the Gulf has been considered eutrophic due to the frequent occurrence of cyanobacteria blooms. This is a major concern since some cyanobacterial species (e.g. Microcystis sp.) have the potential to produce cyanotoxins (Microcystins), putting livestock and humans who rely on these systems for water and food at risk. The cyanobacterial blooms are formed mainly by cyanobacterium Microcystis in the Gulf. High algal biomass has been associated with fish kills, the shutdown of the drinking water treatment plant in Kisumu from January to March 2004 and reports have also shown the occurrence of the cyanotoxins, Microcystins in water and fish. 

The progressive water quality deterioration in the Gulf was partly related to the construction of the Mbita Causeway that linked the Mbita Peninsula and Rusinga Island in 1983. This led to blockage of the Mbita Channel, a secondary passage that connected Rusinga Channel and the offshore waters of Lake Victoria. Fortunately, in May 2017, part of the Causeway was removed and replaced by a Mbita-Rusinga Bridge opening part of Mbita Channel (width, 150 m) to connect the Gulf and the main basin. This was expected to increase water exchange between the Gulf and the main basin and thus improve the water quality and reduce phytoplankton biomass in the Gulf. Preliminary evaluation reports from local fisherman in November 2017 showed that the restoration of the Mbita Channel resulted in increased water transparency, water currents, and increased fish catches. However, there was generally insufficient information on the influence of the main basin on water quality in the Nyanza Gulf based on spatio-temporal variation in physicochemical parameters, phytoplankton biovolume composition and dominance.

Benard Mucholwa Simiyu’s PhD included investigation of the main basin influence on water chemistry and phytoplankton in Nyanza Gulf, using specific conductivity as a tracer, examine the response of planktonic diatom composition to eutrophication in Nyanza Gulf and quantify microcystins (MC) concentrations and other cyanotoxins. Three sampling stations: West Gulf (located near the main basin), Mid Gulf (located at the central part of the gulf) and East Gulf (located close to Kisumu City) were sampled monthly from July 2017 to July 2018. In order to monitor the water exchange with the main basin, specific conductivity and water level were recorded daily from the shore located close to the sampling points. 

Overall, the thesis findings during the observation period 2017–2018 suggest an increased main basin influence on the inner Nyanza Gulf. In particular, the observed dilution at the Eastern part of the Gulf was most likely caused by water exchange with the main basin, which was largely triggered by the overall rise in water level through direct precipitation over the main basin. The enhanced water exchange with the main basin probably resulted in improved water quality conditions and not at least reduction in Microcystis and MC concentrations. These findings provide important information on the general variation in water quality conditions in Nyanza Gulf of Lake Victoria.

The results from this thesis have been published in the peer reviewed journals Great Lakes Research Journal and in the Limnologica journal. The third paper is still in preparation. During his PhD studies, Benard Mucholwa Simiyu was awarded an International Student Travel Scholarship by International Association for Great Lakes Research to attend the 62nd Annual Conference on Great Lakes Research that was held at the College of Brockport, State University of New York, in June 2019. He was also awarded the Tonolli Fund Memorial award from the International Society of Limnology in 2017.

Benard Mucholwa Simiyu is a part time lecturer at the Department of Geoscience and Environment, Technical University of Kenya. He has a background in Aquatic Ecology with a Master of Science Degree in Environmental Sciences, Specialization in Limnology and Wetlands Ecosystems from the Institute for Water Education (UNESCO-IHE), Netherlands. Before he started his PhD, he worked as a Research assistant in the Arthrospira Biomass Dynamics Project in saline Alkaline lakes (Bogoria and Nakuru) at Egerton University. He also worked at the National Environment Management Authority of Kenya where he participated in the process of developing environmental management plans for Lake Olbolossat and Lake Jipe in Kenya and as a part-time lecturer at the Technical University of Kenya. He is a member of the International Society for Limnology (SIL) and International Association of Great Lakes Research (IAGLR).


Simiyu, B. M., Amukhuma, H. S., Sitoki, L., Okello, W., Kurmayr, R. (2021). Interannual variability of water quality conditions in the Nyanza Gulf of Lake Victoria, Kenya. Journal of Great Lakes Research, Vol. 48, Issue 1, 97-109. 

Simiyu, B. M., Kurmayr, R. (2022). Response of planktonic diatoms to eutrophication in Nyanza Gulf of Lake Victoria, Kenya. Limnologica, Vol. 93, Article 125958.