The St. Croix River, its tributary streams and rivers, and Lake St. Croix are highly valued resources that provide exceptional recreational opportunities and support diverse wildlife in and out of the water. However, over the years eutrophication, or nutrient enrichment, has occurred in Lake St. Croix due to increasing amounts of phosphorus entering the lake from the watershed. The elevated level of phosphorus in Lake St. Croix results in algae blooms which diminish the enjoyment and use of the lake and impact the ecologic integrity. Elevated phosphorus levels not only impact Lake St. Croix, but also impact tributary streams, rivers, and lakes throughout the watershed. While progress has been made in recent years to understand and reduce the amount of phosphorus finding its way into streams and lakes, much work remains.
TMDL Actions in Wisconsin
Currently the St. Croix InterAgency Basin Team has developed a detailed monitoring plan for the St. Croix River to facilitate nutrient loading calculations for the TMDL process. The Minnesota Pollution Control Agency, National Park Service, USGS, Metropolitan Council Environmental Services, and MN DNR are actively monitoring 8 priority tributaries and numerous main stem sites within each of their geographic areas. Currently they are collecting standard nutrient parameters (Flow, TP, DP, TN, Nitrate + Nitrite, Ammonia, Total Suspended Solids, and Turbidity) during baseflow and runoff events at the bottom of each sub watershed within their areas. Flow measurements and gauging stations are being used to calculate loads at the time of each sampling event. Additional biological monitoring (Ffsh and invertebrates) are being collected at each of their respective monitoring sites. Before an accurate TMDL can be calculated, the Wisconsin tributaries to the St. Croix need similar nutrient monitoring data linked with flows to accurately calculate loads for a fully integrated TMDL calculation.