Technical Abstract: The Cannonsville Reservoir, a Conservation Effects Assessment Project (CEAP) benchmark watershed, is a major component of the unfiltered New York City water supply system. The voluntary, incentive-based Watershed Agricultural Program is a collaborative effort among producers, federal, state, and local organizations to address the problem of phosphorus (P) loading effects on water quality through implementation of whole farm plans. Collaborative Agricultural Research Service and Cooperative State Research, Education, and Extension Service funded, CEAP-related research is documenting the effectiveness of selected conservation practices, including stream bank fencing, precision feeding, and the use of cover crops with silage corn. Modeling efforts have assessed the effectiveness of individual conservation practices and the aggregate effects on water quality at farm and watershed scales. Models have been developed and improved to better assess animal agriculture and manure management practices. Conservation practices implemented through the Watershed Agricultural Program are resulting in lower P loading from non-point sources in the Cannonsville Reservoir Watershed. The challenge for CEAP is to identify the most cost-effective conservation practices and extend our knowledge of watershed quality protection beyond the boundaries of the Cannonsville Reservoir Watershed, thereby lowering the costs of water quality protection so that other watersheds where public resources are limited can also meet reasonable water quality standards.