A phosphorus reduction strategy for Lake Champlain was selected through three major steps. The first step was an agreement on the phosphorus concentration goals for the segments of Lake Champlain among New York, Vermont and Quebec. Next, a phosphorus budget for the Lake was developed and the reductions needed to meet the agreed upon phosphorus concentration goals were determined. Lastly, a cost optimization procedure to select the most cost-effective reduction strategies was developed and the reduction strategy was selected. More information is below regarding the phosphorus criteria, budget, and cost-effectiveness strategies.

Of additional importance to phosphorus reduction on Lake Champlain were the development of the TMDL for the Lake by New York and Vermont and the Missisquoi Bay Phosphorus Agreement between Vermont and Quebec.

In 1993, New York, Vermont and Quebec signed a Water Quality Agreement committing the three entities to use a consistent approach to phosphorus management. The agreement defined in-lake phosphorus concentration criteria (standards) for thirteen lake segments, establishing the phosphorus concentrations to be sought in each segment. For more information on the criteria for the thirteen lake segments, view the Phosphorus Concentration page and map on the LCB Atlas, which shows the phosphorus criteria for each Lake segment and the phosphorus levels.

The states of Vermont and New York completed a study to measure point and nonpoint source phosphorus loads to the Lake, develop a whole-lake phosphorus budget, and develop a load reduction strategy to attain the in-lake criteria (Vermont Department of Environmental Conservation and New York State Department of Environmental Conservation, 1994). The results of this study (called the "Lake Champlain Diagnostic-Feasibility Study") indicate that the annual phosphorus load to the Lake needs to be reduced by another 57 metric tons (relative to the 1995 load) in order to attain the in-lake criteria. This represents about 11 percent of the estimated 1995 total of 496 metric tons introduced to the Lake each year.

In 1995, Holmes and Artuso developed an optimization procedure to determine the cost-effectiveness of various strategies for attaining the in-lake phosphorus criteria (Holmes and Artuso, 1995). Designed for use with the phosphorus model for Lake Champlain, the optimization procedure takes into account the costs of potential phosphorus reductions achievable from agricultural and urban land as well as the manner in which changes to phosphorus levels in each lake segment are expected to affect phosphorus levels in all other lake segments. The procedure allows one to sort through he multitude of possible combinations of point and nonpoint source reductions that are predicted to attain the in-lake criteria.

In early 1996, representatives from the states of Vermont and New York and USEPA used the phosphorus model and cost optimization procedure to develop a new bi-state process for phosphorus reductions. Following extensive analysis of numerous reduction scenarios, the group selected a load reduction process, considered both fair and cost-effective, which was endorsed by the Lake Champlain Management Conference. The agreed upon process targets 12 of 19 watersheds for phosphorus reductions. Contingent on the availability of federal and/or state funds, each state will reduce the difference between existing (1995) loads and target loads by at least 25% per five year period for the next 20 years. For more information on the existing and target loads for each lake segment, view the the Phosphorus Loads page and map on the LCB Atlas. Also view the Point and Nonpoint phosphorus pages and maps on the Atlas for more source information.

The states are free to choose the appropriate mix of point and nonpoint source actions to be implemented in each of the watersheds. States will also have the opportunity to adjust the total loading targets for each of the watersheds, as long as the adjusted loads continue to meet the in-lake phosphorus concentration goals and each state keeps the other state's allowable loads fixed. The adjusted loads for each state will then be checked together to ensure that the in-lake goals will be achieved.