Lake Naivasha in Kenya is an important livelihood resource for its adjacent communities. However, this freshwater lake is under significant strain due to anthropogenic activities. The study aimed to determine the water quality status of Lake Naivasha in order to establish its trophic state. Physico-chemical parameters were studied in seven pre-defined stations in the main lake from February to July 2019 (autumn and winter months). Monthly samplings were done and sample analyses using standard procedures were undertaken. Samples were collected in triplicates for the determination of nitrate nitrogen, soluble reactive phosphorous, total nitrogen (TN), total phosphorous (TP), ammonium nitrogen, silicates, and chlorophyll a. Water temperature, conductivity, dissolved oxygen (DO), and pH were measured in situ using a multimeter probe. The results showed the mean water temperature to be 22.73 ± 1.6 °C, DO 8.51 ± 0.87 mg/L, conductivity 233.85 ± 26.94 μS/cm, pH 8.13 ± 0.3. TN were 471 ± 170.61 µg/L, PO4 5.88 ± 2.12 µg/L, TP 97.97 ± 49.06 µg/L, NO3-N 6.70 ± 3.55 µg/L, NH4-N 18.93 ± 10.91 µg/L, SiO2 3.18 ± 2.99 mg/l and Chlorophyll a 21.51 ± 4.25 Mg/m³. The study revealed that secchi depth, total phosphorous, and chlorophyll a showed significant differences spatially (P = 0.05). The results imply that Lake Naivasha is contaminated with pollutants from domestic wastewater, agricultural and/ or surface run off. A sewage discharge point and the R. Malewa mouth were identified as the main point sources of pollution. Therefore, there is a need for measures to be put in place to reduce water contamination from these points in order to improve the water quality of the lake.

Keywords: Nutrients, Anthropogenic activities, Water quality, Ecosystem, Lake Catchment