Multivariate analysis of benthic data, as major taxa, from a study of ecological impacts of pollution in Jakara reservoir showed that Axis 1 of NMDS ordination of the sampling sites accounted for 55.3% of the variation in spatial distribution of the organisms while Axes 2 and 3 accounted for 32.6% and 12.1% respectively. As genera, Axes 1, 2 and 3 accounted for 60.3%, 21% and 18.7% of the variation respectively. In both cases the sites exhibited a high degree of homogeneity in biotic distribution and the discrimination of the sites was not different.

The Coefficient of Multiple Determination (R2), of the Multiple Linear Regression of 11 environmental parameters upon the first 3 components of the ordination of the benthic data as major taxa indicated very high (0.81), average (0.41) and low (0.37) relationships between environmental parameters and the spatial distribution patterns. These coefficients are very highly significant (p < 0.001) and to them, P (48%), Water Content (40%) and Zn (68%) contributed highest respectively. Interpretations of these results implicated P as the most important source of sediment-related ecological stress and the order of importance of environmental factors in affecting the ecology of the reservoir was (1) factors related to nutrient enrichment from organic pollution, (2) factors related to the physical environment, and (3) factors related to toxic pollution.

Only Chironomids, Oligochaetes and Heleidae were found and these were dominated by CHIRONOMUS spp. (70%), TUBIFEX spp. (13%) and LIMNODRILUS spp. (4%). The 24 months of study were grouped into the annual rainy and dry season months or the low water and flood periods with respect to the seasonal distribution of the organisms which was found, through Principal Component Analysis, to be controlled mostly (45%) by the conductivity of the overlying water which remained at pollutant levels throughout. Annual mean density of benthos was 8469 organisms per square meter. About 0.7 centimeters (cm) of sediment, consisting of 59 to 80% clay and 20 to 30% silt is formed annually. The discontinuity layer was located between 1 and 6 cm and organisms, especially Oligochaetes, penetrated to these depths in some sites.

Annual mean input of P was 0.58 milligrams (mg) per liter. Application of the Vollenweider Relationship confirmed that the reservoir is hyper-eutrophic. Mean metal concentrations in water were: Zn, 0.145; Mn, 3.195; Hg, 0.607; Pb, 0.032; Cd, 0.005 and As, 0.005 mg per milliliter. Computed Risk Factors (RF), based on the US-EPA limits for safety of aquatic life, showed that Hg, Cd, Pb and Zn have RFs of 3,035, 125, 8 and 3 respectively. Mean metal concentration in the sediment were high: Zn, 1.122; Mn, 5.337; Hg, 0.984; Pb, 0.420; Cd, 0.047 and As, 0.078 milligrams per gram dry weight.

Restoration could be achieved through biological extraction of the pollutants in the inflow using Duckweed. It was estimated that if 3% of the annual run-off into the reservoir is subjected to a residence time of 10 days under a full cover of Duckweed, the levels of P in the water would be reduced to 0.08 mg per liter which is sufficient to restore the reservoir to oligotrophy.