Water samples from Msimbazi and Kizinga rivers in Dar es Salaam and from the coastal marine environment receiving waters from these rivers were analyzed for various organochlorine pescticide residues using GC-ECD and GC-MS. p,p'-DDE, p,p'-DDT, dieldrin and γ-HCH were the only organochlorine pesticide residues detected at significantly greater concentrations above the detection limits. There was a marked difference in the frequency of pesticide residue detection during the dry and wet seasons. All the wet season samples and 37.5% of the dry season samples revealed presence of p,p-DDE at concentrations ranging from 0.05 to 0.45 mgl-1 and 0.08 to 0.20 mgl-1 respectively. pp'-DDT was detected in 25% of the dry season samples at a concentration range of 0.1-0.4 mgl-1 and in 81% of the wet season samples at concentrations ranging from 0.1 – 0.3 mgl-1. Dieldrin and γ-HCH were only detected during the wet season. Dieldrin amounts ranging between 0.2 and 2.5 mgl-1 were detected in all wet season samples whereas γ-HCH (0.2 mgl-1) was found in only one wet season sample. Recoveries of pesticides ranged from 65 to 108%. The present study suggests that the current levels of pesticides detected in these waters have no acute effects to aquatic biota. However, the levels of total DDT and dieldrin present during the wet season suggest a possibility for chronic effects on aquatic biota.