Centerville Lake Internal Phosphorus Load Reduction Project

Centerville Lake is located in the cities of Centerville and Lino Lakes, two fast-growing communities in the northern Twin Cities Metro Area. This highly-used regional resource is home to the Rice Creek Chain of Lakes Park Reserve, the largest park in the Anoka County Parks system, tallying over 700,000 visits per year. Unfortunately, Centerville Lake experiences frequent and severe algae blooms, and needs assistance to meet state water quality standards and user expectations. The lake is listed as impaired for excess nutrients; average summer phosphorus and chlorophyll-a concentrations exceed the state standards by a factor of two. Facilities at the Rice Creek Chain of Lakes Park Reserve are often closed due to health concerns associated with blue-green algae blooms. Much work has been done over the past 15 years to diagnose and control nutrient loading. Following the completion of the TMDL study, multiple watershed phosphorus management projects were completed, including standard stormwater BMPs (e.g. raingardens, biofiltration basins, and wet ponds) and a significant stormwater reuse project. Despite these efforts, water clarity remains poor, and algae blooms continue. More recently, the Rice Creek Watershed District (RCWD) completed a series of diagnostic studies to better understand the sources and magnitude of nutrient loads. These studies show that internal phosphorus loading - specifically, sediment-phosphorus release - is the primary nutrient source for Centerville Lake, and the primary driver of the severe algae blooms. The Rice Creek Watershed District is proposing to control internal phosphorus loading by inactivating sediment phosphorus with aluminum sulfate (alum). The proposed alum treatment targets the largest source of phosphorus to Centerville Lake, and is the most impactful and cost-effective tool available to restore water clarity in Centerville Lake. Factors that could negatively affect the longevity of the proposed alum treatment were assessed (i.e. common carp and watershed loading), and found to be negligible. The proposed project will provide control of sediment phosphorus release and result in attainment of state water quality standards. Most importantly, the proposed project will control nuisance algae blooms, restoring an important and highly-used regional resource.