Skip to main content
U.S. flag

An official website of the United States government

Nationwide assessment of nonpoint source threats to water quality



Publication type:

Scientific Journal (JRNL)

Primary Station(s):

Rocky Mountain Research Station


BioScience. 62(2): 136-146.


Water quality is a continuing national concern, in part because the containment of pollution from nonpoint (diffuse) sources remains a challenge. We examine the spatial distribution of nonpoint-source threats to water quality. On the basis of comprehensive data sets for a series of watershed stressors, the relative risk of water-quality impairment was estimated for the over 15,000 fifth-level watersheds in the contiguous United States. A broad division emerged at about the 100th meridian, with eastern areas typically under higher stress than western areas, reflecting the generally higher housing, road, and agriculture densities and higher levels of atmospheric deposition in the eastern division. Recent trends in some stressors are encouraging, but the prospect of further substantial population growth indicates continued pressure on water quality, suggesting that renewed focus on controlling nonpoint-source pollution will be needed if the goals of the Clean Water Act are to be attained.


Brown, Thomas C.; Froemke, Pamela. 2012. Nationwide assessment of nonpoint source threats to water quality. BioScience. 62(2): 136-146.

Publication Notes

  • We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
  • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.