Water quality monitoring data is collected in priority tributaries as part of binational efforts under Aneex 4 of the Great Lakes Water Quality Agreement (GLWQA) to estimate nutrient loading to the waters of the Great Lakes. At present, the focus is primarily tributaries of Lake Erie, the smallest, shallowest of the Great Lakes, and most susceptible to algal blooms. Tributaries may be added or removed from active monitoring dependent upon recommendation of binational working groups under the GLWQA. These data are used to track and report on progress towards meeting nutrient loading targets established for Lake Erie. The data also contribute to our understanding of the factors that affect tributary and nearshore and offshore water quality, algae growth and overall ecosystem health.