"The principal law governing pollution of the nation's surface waters is the Federal Water Pollution Control Act, or Clean Water Act. Originally enacted in 1948, it was totally revised by amendments in 1972 that gave the act its current shape. The 1972 legislation spelled out ambitious programs for water quality improvement that have since been expanded and are still being implemented by industries and municipalities. […]The Clean Water Act consists of two major parts, one being the provisions which authorize federal financial assistance for municipal sewage treatment plant construction. The other is the regulatory requirements that apply to industrial and municipal dischargers. The act has been termed a technology-forcing statute because of the rigorous demands placed on those who are regulated by it to achieve higher and higher levels of pollution abatement under deadlines specified in the law. Early on, emphasis was on controlling discharges of conventional pollutants (e.g., suspended solids or bacteria that are biodegradable and occur naturally in the aquatic environment), while control of toxic pollutant discharges has been a key focus of water quality programs more recently. Prior to 1987, programs were primarily directed at point source pollution, wastes discharged from discrete sources such as pipes and outfalls. Amendments in that year authorized measures to address non-point source pollution (stormwater runoff from farm lands, forests, construction sites, and urban areas), now estimated to represent more than 50% of the nation's remaining water pollution problems."
CRS Report for Congress, RL30030
National Agricultural Law Center http://www.nationalaglawcenter.org/crs/