Fish kills in lake Naivasha, Kenya: What was the probable cause?

Fish kills were detected in Lake Naivasha in February 2010. Physico-chemical parameters and pesticide residue screening were done to ascertain if they contributed to the kills. Mean (±SD) dissolved oxygen, temperature, pH and conductivity were 4.06 ± 1.97 mgl -1 , 24.63 ± 1.58 0 C, 8.74 ±0.85 and 303.29 ± 76.20 µScm -1 respectively. Except for conductivity, all parameters were significantly different between months (p 0.05). There were detectable levels of organochlorines in fish fresh while sediment samples had pesticides below limit of detection. The majority of dead fish were Cyprinus carpio. Fish examined showed no external damage and on dissection, appeared to be in good physical condition, pointing to the effects of water quality rather than poisoning on their deaths. There are indications that Lake Naivasha is becoming hyper-eutrophic. Firm measures to reduce nutrients entry into the lake should be instituted to reduce deterioration in water quality.