The Awba stream enters the lake just before Zone A and flows across Zones B and C with a velocity of about 0.61 m/s. The results of analyses of samples of water collected below the layer of Pistia plants (about 30 cm deep) at Zones A, B and C are given in Table 4. The results indicate that at Zone A the mean values for pH, dissolved oxygen and BOD were higher in the dry season than in the wet season. However, the mean values for organic matter which is resistant to oxidation (4-h PV), ammonia nitrogen, water-soluble phosphorus, alkalinity, calcium and magnesium were higher in the wet season, possibly due to storm water. In Zones B and C there were comparatively fewer pollutants but the seasonal variation was similar to that of Zone A. The results indicate the quality of water as it existed as a result of Pistia growth and multiplication.