Water quality in Iowa is measured by comparisons of recent monitoring data to the Iowa Water Quality Standards. Results of recent water quality monitoring, special water quality studies, and other assessments of the quality of Iowa's waters are used to determine the degree to which Iowa's rivers, streams, lakes, and wetlands support the beneficial uses for which they are designated in the Iowa Water Quality Standards (for example, aquatic life (fishing), swimming, and/or use as a source of a public water supply). Other information from water quality monitoring and studies that are up to five years old are also used to expand the coverage of assessments in the report. Waters where one or more designated use has been determined to be not supported are assessed as impaired, and form the basis for the state's list of impaired waters as required by Section 303(d) of the Clean Water Act.
Summaries of Section 305(b) assessments for all states are available from U.S. EPA.