Heavy metal pollution may pose a significant threat to aquatic ecosystems. To assess heavy metal pollution, sediment samples were collected from Changwang and Wuyuan Rivers between June and December 2019. An inductively coupled plasma mass spectrometer was used to analyze the concentrations of As, Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn. The results revealed that Changwang River had significantly high concentrations of Cr (240.70 mg kg⁻¹), Co (36.02 mg kg⁻¹), Ni (108.70 mg kg⁻¹), and Cu (36.61 mg kg⁻¹), whereas As (7.55 mg kg⁻¹) was elevated in Wuyuan River. In addition, Cd, As, Pb and Zn concentrations were below China’s sediment quality standard limits (GB 3838-2002), but the Cr level exceeded the limit. However, Cr and Ni exceeded the probable effect concentrations (PEC) and thus may cause toxic effects. The contamination factor, geo-accumulation index, and modified degree of contamination revealed that Changwang experienced considerable to very high heavy metal pollution, while Wuyuan had low to moderate pollution. The pollution load index demonstrated that the rivers were polluted during all seasons. Additionally, the risk index showed considerable and moderate risks in Changwang and Wuyuan, respectively. The metal ecological risk was ranked as Cd > Ni > As > Co > Cu > Cr > Mn > Pb > Zn. Multivariate analyses categorized heavy metals into two groups based on their potential sources: group one included Cr, Co, Ni, Cu, Mn, and Zn, while group two contained As, Cd, and Pb. The study provides valuable data on heavy metal pollution, which needs improvement for the studied rivers. The data can be used to assess pollution risks and manage riverine sediment quality.

Oreochromis leucostictus is one of the commercially important tilapiine in Lake Naivasha. Its stock in the lake has declined due to the effect of fishing and pollution. This study investigated on its length-weight relationship, condition factor, sex ratio and maturity. Fish samples (233) were caught using gillnets of mesh-sizes 2-5 inches. Each individual fish was measured (cm) and weighed (g) in the field. The specimens were preserved in ice and transported to the laboratory for analysis of maturity. The mean (±SE) total length and weight for all fish was 21.3±0.3 cm TL and 187.4±8.3 g, respectively. Males 22.3±0.4 cm were significantly larger than females 19.2±0.5 cm. The mean condition factor was 1.06, 0.99 and 1.04 for male, female and combined sexes, respectively. The overall population sex ratio was 2.19:1.0 (male: female) that deviated significantly from 1:1. The slope b of the length-weight relationship was 1.92, 3.07, 2.33 for males, females, and combined sexes, respectively. Length at 50% maturity was estimated at 21.0 cm for females and 26.0 cm for males. Ripe oocytes and testis were found in all fish sizes. Comparisons with earlier studies suggest that the parameters of its growth, condition and maturity vary greatly from the different habitats.