tors of poor ecological health. The large amounts of algal material produced under these conditions also deplete oxygen concentrations as the algae die and decompose. This can cause or aggravate problems of low DO in bottom waters. TVA results indicate that a mean summer chlorophyll-a concentration greater than 15 μg/l is a threshold above which these undesirable conditions are likely.

These threshold levels are incorporated into the chlorophyll-a ratings at each sampling location (Table 3). The average summer chlorophyll-a concentration of monthly photic zone samples collected from April through September (or October) is compared with these criteria and rated accordingly.

Contaminated bottom sediments can have direct adverse impacts on bottom fauna and can often be long-term sources of toxic substances in the aquatic environment. Wildlife and humans may be affected by these contaminants by ingestion or through direct contact. These effects may occur even though the water