The decline in DO that was recorded could not be directly related to any one environmental factor, but a combination of nutrients may have boosted the growth of macrophytes and filamentous algae over the long term. Data on the biomass of macrophytes and filamentous algae were not available for this study. However, recommended maximum concentrations of TON, total phosphorus and SRP, in order to keep filamentous algal biomass at manageable levels below 100 mgm2 [19], were exceeded at several sites on a regular basis [10].