According to the U.S. Environmental Protection Agency (EPA), half of U.S. rivers, lakes, and streams and 60% of bays and estuaries are impaired by nutrients from urban and agricultural runoff and other sources. The Association of Clean Water Administrators (ACWA) recently released a survey on the use of biological indicators in state water programs. The survey shows that while many states use biological criteria, along with nutrient concentrations, to assess whether a waterbody is nutrient-impaired, only a handful use these criteria in their National Pollutant Discharge Elimination System (NPDES) permits. However, such criteria could offer an alternative to numeric criteria. Florida uses biological assessments as part of its NPDES permit to determine whether facilities are complying with criteria designed to protect aquatic life. Georgia uses biological criteria in its industrial stormwater permit and has developed a nutrient pollution tolerance index for aquatic life. Facilities located within a linear mile (1.6 km) of an impaired stream are required to sample for macroinvertebrates or another biological parameter of concern, chlorophyll a, which can indicate large populations of algae that thrive on nutrients.