ABSTRACT: Controlling agricultural nonpoint source pollution from livestock grazing is a necessary step to improving the water quality of the nation’s streams. The goal of enhanced stream water quality will most likely result from the implementation of an inte- grated system of best management practices (BMPs) linked with stream hydraulic and geomorphic characteristics. However, a graz- ing BMP system is often developed with the concept that BMPs will function independently from interactions among controls, climatic regions, and the multifaceted functions exhibited by streams. This paper examines the peer reviewed literature pertaining to grazing BMPs commonly implemented in the southern humid region of the United States to ascertain effects of BMPs on stream water quality. Results indicate that the most extensive BMP research efforts occurred in the western and midwestern U.S. While numerous stud- ies documented the negative impacts of grazing on stream health, few actually examined the success of BMPs for mitigating these effects. Even fewer studies provided the necessary information to enable the reader to determine the efficacy of a comprehensive sys- tems approach integrating multiple BMPs with pre-BMP and post- BMP geomorphic conditions. Perhaps grazing BMP research should begin incorporating geomorphic information about the streams with the goal of achieving sustainable stream water quality. (KEY TERMS: sustainability; agriculture; environmental impacts; water quality; nonpoint source pollution; best management prac- tices.) Agouridis, Carmen T., Stephen R. Workman, Richard C. Warner, and Gregory D. Jennings, 2005. Livestock Grazing Management Impacts on Stream Water Quality: A Review. Journal of the American Water Resources Association (JAWRA) 41(3):591-606. INTRODUCTION Animal agriculture is a significant component of U.S. agricultural sales, accounting for over 50 percent of the nearly $200 billion in agricultural products sold (USDA-NASS, 1997). Beef cow/calf production alone generated $40.5 billion in sales. Dairy cattle and their associated products (i.e., milk, cream, and butter) along with horses accounted for over 11 percent of sales. In the southern humid region of the U.S., these 14.6 million large grazing animals are a dominant source of income with a total market value of $2.9 bil- lion. Considering the large amount of pastureland and grazed forested lands (15.8 million hectares) in the southern humid region along with the nearly one million kilometers of streams, the potential for dam- age to riparian ecosystems from uncontrolled live- stock access is quite high (Vesterby and Krupa, 1997; USEPA, 2000). For purposes of this paper, the south- ern humid region is defined as Alabama, Florida, Georgia, Kentucky, Louisiana, Mississippi, North Car- olina, South Carolina, Tennessee, Virginia, and West Virginia. Over 36 percent of the assessed rivers and streams in the southern humid region are classified as impaired meaning that they do not fully support one or more designated uses. The U.S. Environmental Protection Agency (USEPA, 2000) noted that the most common pollutants to the southern humid region’s rivers and streams included pathogens, siltation, habitat alterations, organic enrichment, and nutri- ents. Sources of these pollutants, while often difficult to identify, were attributed primarily to agriculture, hydromodifications including flow regulation and modification, channelization, dredging, dam construc- tion, grazing, and habitat modifications including bank destabilization and removal of riparian vegeta- tion (other than flow). Underscored by the significant 1 Paper No. 04076 of the Journal of the American Water Resources Association (JAWRA) (Copyright © 2005). Discussions are open until December 1, 2005. 2 Respectively, Engineer Associate, Associate Professor, and Extension Professor, University of Kentucky, Department of Biosystems and Agricultural Engineering, 128 C.E. Barnhart Bldg., Lexington, Kentucky 40546; and Professor, University of North Carolina, Biological and Agricultural Engineering, Box 7912, Raleigh, North Carolina 27695 (E-Mail/Agouridis: cagourid@bae.uky.edu). JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 591 JAWRA JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION JUNE AMERICAN WATER RESOURCES ASSOCIATION 2005 LIVESTOCK GRAZING MANAGEMENT IMPACTS ON STREAM WATER QUALITY: A REVIEW 1 Carmen T. Agouridis, Stephen R. Workman, Richard C. Warner, and Gregory D. Jennings 2