Lakes in the northeast are generally healthy, with conditions worsening as you move south and west. Lake health corresponds to ecoregions and the differences in soils, climate, lake depth, and size of the lake watershed, as well as land use and alterations. In the parts of the state with the most cultivated land or urbanization, lakes are more likely to test above standards for pollutants.
- In the last two decades, overall lake quality trends have stabilized — the vast majority of lakes’ water quality measures have stayed about the same.
- The water quality of lakes in Minnesota is similar to lakes in our region and nationwide.
- Phosphorus is the contaminant of greatest concern in Minnesota lakes.
- Chloride in lakes from road salt — in urban areas and near roads — is increasing and is especially troubling, because it stays in the water indefinitely.
Current regulations and voluntary best management practices will not be sufficient to maintain healthy lakes and shield impaired ones from additional pollution. Even if all existing laws were followed to the letter, lakes would still be subject to unacceptable levels of nutrients and other contaminants. Targeted action will be required to cut off unregulated sources of pollution.
North-northeastern region and the Arrowhead
After being heavily logged historically, this region is now dominated by forest (41% of the land) and water and wetlands (more than 48%), which limits sediment and nutrient runoff.
In the watersheds the MPCA has fully assessed in the region, 92% of the lakes meet water quality standards for aquatic recreation.
Central region and metro area
Land use threats
This area combines characteristics of both the northeastern and southern regions. Shallow lakes here that are in highly urbanized or heavily farmed watersheds typically have poor water quality. Deeper lakes, or those in watersheds with less urbanization or agricultural land use, generally have better water quality.
Half are impaired
In the watersheds the MPCA has fully assessed in the region, 50% of the lakes meet water quality standards for aquatic recreation.
Southern and western Minnesota
Much of this region’s prairie has been converted to agricultural uses (78% is cropland), while wetlands have been drained and the installation of artificial drainage has increased. This has caused high nutrient and sediment levels in the region’s naturally shallow lakes.
In the watersheds the MPCA has fully assessed in the region, only 18% of the lakes meet water quality standards for aquatic recreation.
Ten Mile Lake near Hackensack is among the largest and deepest lakes in Minnesota. At this time, the lake is free of aquatic invasive species and has a watershed dominated by forest. Development pressure is light. Water quality is excellent.
Medicine Lake in Plymouth is in a watershed that is entirely developed, with the exception of a park on the north end of the basin. The lake has excess levels of phosphorus — which contributes to nuisance algal blooms in the summer — and high chloride concentrations, which can stress fish. It also has Eurasian milfoil, an invasive species.
South and west region
Lake Shaokotan near Ivanhoe is in a watershed dominated by agricultural land uses. Considerable work has been done to improve water quality in the lake, but phosphorus concentrations remain high and algal blooms are common.