When lakes and rivers are polluted with phosphorus, sediment, and other contaminants, it can take years of sustained effort and expense to restore the water quality. Counties, cities, watershed districts, and other organizations and individuals have taken on these restoration efforts around the state, and they are having an impact. For instance, some metro-area lakes are meeting water quality standards that they failed to meet previously, all thanks to the work of community governments and organizations.
The Minnesota Pollution Control Agency added Crystal Lake in Burnsville and McMahon Lake in Scott County to the state’s “impaired waters” list in 2002 because testing showed levels of phosphorus in the water that exceeded state standards. Bryant Lake in Eden Prairie got on the list in 2008 for the same reason.
Phosphorus can get into lakes, rivers, and streams from a variety of sources, but the most common are runoff (or stormwater) from farmland and urban areas, stream bank erosion, treated wastewater from both public and private facilities, and airborne sources such as wind-blown soil. Phosphorus sinks into sediments in lake bottoms and can be re-released over time by fish activity and other agitation. Phosphorus fuels algae blooms that interfere with recreational activities like boating and swimming. Sometimes harmful blue-green algae form, which can sicken people and their pets.
What strategies can reduce phosphorus and restore a lake’s water quality? Many communities focus on their stormwater practices. The rain and snow melt running into storm drains from streets, parking lots, and other hard surfaces can contribute leaves, oils, lawn chemicals, and other contaminants to nearby lakes. Directing stormwater to places it can soak into the ground and where contaminants can be filtered out can go a long way to reducing pollution. The MPCA regulates municipal stormwater and requires cities and towns to educate citizens on stormwater management, make plans to detect and stop illicit discharges, control runoff on construction sites, and more.
To reduce phosphorus in Crystal Lake, the city of Burnsville built an underground system to treat stormwater before it’s discharged into Keller Lake (which feeds into Crystal Lake). The city of Apple Valley built a stormwater pond on Keller Lake that keeps an estimated 55 pounds of phosphorus out of the water every year. Water monitoring showed that 20% to 25% of phosphorus in Crystal Lake was coming from Keller Lake. In addition, Lakeville and Burnsville dredged some existing stormwater ponds near Crystal Lake, which improves the ponds’ filtering ability and makes them more efficient. For Bryant Lake in Eden Prairie, new stormwater standards adopted in 2008 have helped improve the lake’s water quality. The project partners also restored wetlands just west of the lake, which helps control stormwater as well.
Addressing shoreline degradation is another way to help lakes. An eroding shoreline can contribute sediment and soil to lakes, which can increase phosphorus levels. A project by the Scott Soil & Water Conservation District and a shoreland property owner used large rocks and rolls of coconut fibers called coir logs to stabilize vulnerable shoreline on McMahon Lake. Vertical banks were graded into gradual slopes with native plants to sustain the shoreline and protect the lake.
Harvesting curly leaf pond weed is another restoration strategy the City of Burnsville used to improve Crystal Lake. The city hired machines that spent two weeks cutting back the plant over about 50 acres of the 290-acre lake. If not cut back, the weed would die off in the peak of summer, releasing nutrients into the water that feed algae blooms.
The Nine Mile Creek Watershed District in Eden Prairie undertook in-lake treatments to help reduce phosphorus in Bryant Lake. In 2008 and 2013, the district treated the lake with aluminum sulfate (called alum), which forms a fluffy substance called floc. As the floc settles to the lake bottom, it removes phosphorus and other materials (including algae) from the water. The floc forms a layer over the sediment that acts as a barrier to phosphorus. It binds phosphorus released from the sediment and prevents it from fueling algae blooms.
All the lake cleanup projects relied on multiple players in addition to those already mentioned. Black Dog Watershed Management Organization helped to do water monitoring, organize projects, and apply for grants to benefit Crystal Lake. The city of Eden Prairie and Three Rivers Park District have assisted in monitoring Bryant Lake and making project recommendations. The Scott Watershed Management Organization, the New Market Sportsman’s Club, and shoreland owners participated in the cleanup of McMahon Lake.
And the cleaner lakes are a boon to their communities. “Overall, Crystal Lake now has a higher value to residents,” says Daryl Jacobson, Natural Resources Manager with the city of Burnsville, who led the water quality improvement efforts. Paul Nelson, Environmental Services Program Manager with Scott County and coordinator for the McMahon Lake work, says the lake is more attractive for swimming and other recreation, and is a source of local pride.
These organizations are also working to restore water quality in several other lakes and streams. So their work identifying and remedying sources of water pollution will continue.