Across the nation, nutrients are reported frequently as a cause of impairment of surface waters. For example, in EPA’s 1998 National Water Quality Inventory, nutrients were identified as contributing to impairment in 30% of the streams reported as impaired and 44% of the lakes reported as impaired.. Under Section 303(c) of the Clean Water Act, States are required to develop criteria for those pollutants that could cause or contribute to impairment of surface waters.