River and tributary water quality is critical to maintain the diverse aquatic ecosystem of the St. Croix River, in particular the lower 40kilometersthat make up Lake St. Croix. The high-quality fish habitat of the St. Croix National Scenic Riverway has been designated “Outstanding Resource Waters” by both Wisconsin and Minnesota.

However, persistent cyanobacterial harmful algal blooms (HABs) that occur frequently in Lake St. Croix threaten this designation. Cyanobacterial HABs are a significant issue for the Park because of the potential toxins produced by cyanobacteria that introduce a health threat for visitors and wildlife.

This research will fill a critical knowledge gap for Lake St. Croix to better understand the drivers of cyanobacterial HABs and their potential toxicity. An existing Lake St. Croix water-quality model will be enhanced to evaluate the continuous biomass of multiple cyanobacteria genera within Lake St. Croix. This will allow SACN to better predict and manage the risk assessment for Park visitors.