Halsteds Bay is located at the far west end of Lake Minnetonka. This 544-acre bay is relatively shallow (maximum depth is 36 ft, average depth is 13 ft) and hypereutrophic-meaning that it is a very fertile and productive water body (it grows a lot of algae). The bay received raw and partially treated sewage inputs until sewage discharge into the lake was outlawed in 1969.

Development along the shoreline consists of 143 homes, all of which are sewered. A great deal of the shoreline consists of wetlands and the Lake Minnetonka Regional Park takes up a portion of the southern shore.

Halsteds Bay experiences intense algal blooms in the summer. Algae are single-celled plants that need sunlight, carbon dioxide and nutrients to grow. Usually, the fertility of the lake is controlled by the concentration of nutrients in the water-most often phosphorus in the metro lakes. In historically polluted lakes, phosphorus is delivered to the lake in runoff from the watershed (via erosion, lawn fertilizer runoff and sheet runoff), but also from "below"-from the phosphorus that has accumulated in the sediments and is released when the oxygen is depleted.

We were interested in the potential for intermittent wind mixing to cause temporary breakdowns in thermal stratification in Halsteds Bay. This mixing can inject high phosphorus/low oxygen bottom water up into the sunlit euphotic zone, which can trigger algal blooms.

The RUSS unit is key in determining when these mixing events occur because it can sample the entire water column every few hours, even during storms when it would be dangerous for limnologists to sample.

See how storms influence the water quality in Halsteds Bay.