The nation's aquatic resources are among its most valuable assets. Although environmental protection programs in the United States have successfully improved water quality during the past 30 years, many challenges remain. Significant strides have been made in reducing the impacts of discrete pollutant sources, but aquatic ecosystems remain impaired, primarily because of complex pollution problems caused by nonpoint source (NPS) pollution. This guidance document describes practices to reduce NPS pollution of surface waters and ground water through the protection and restoration of wetlands and riparian areas, as well as the implementation of vegetated treatment systems. The guidance provides background information about NPS pollution, including where it comes from and how it enters the nation's waters; discusses the broad concept of assessing and addressing water quality problems on a watershed level; and presents recent technical information about how certain types of NPS pollution can be reduced effectively through the implementation of these management measures.