In a bright spot of 2020, both Spring and Prior Lakes saw improved water quality this year which was a boon to everyone who swarmed to the lake this summer for swimming, fishing and boating. This year marked the first time that all three water quality standards – the goal for a healthy lake – were met on either Spring Lake or Upper Prior Lake.
In the graphs shown below you can see how the levels for each of three water quality parameters have generally improved over time for each lake. The dashed lines show the water quality standards – the goal to meet for good water quality.
Water clarity (Secchi disk depth), total phosphorus concentration and chlorophyll-a concentration are the main standards used by the state of Minnesota to determine if the water quality in a lake is classified as impaired. Check out our Water Quality Report Cards for quick explanations of the water quality indicators. Spring Lake and Upper Prior Lake were designated as impaired waters in 2002 as a result of high nutrient levels (phosphorus) in the lakes.
Projects Improving Water Quality
The District has been working hard to improve the water quality on the lakes through a number of projects with the goal of having the lakes removed from the State’s impaired waters list. The District has implemented projects and worked with local partners to improve water quality and reduce nutrient levels in the lakes including:
- Ferric chloride treatment facility
- CR 12/17 wetlands restoration project
- Restoring wetlands upstream
- Carp management program to remove invasive common carp
- Street sweeping to reduce nutrients entering the lakes (with the City of Prior Lake)
- Working with farmers to implement best management practices such as cover crops, nutrient management & buffers
- Restoring shoreline habitat including the Spring Lake parcel and Raymond Park restoration projects
- Providing assistance to residents to install raingardens and restore lake shorelines
Reducing Phosphorus with Alum Treatments
In 2020, the District also did an alum treatment on both Spring and Upper Prior Lakes – a first for Upper Prior. Over time phosphorus entering the lake from external sources like streams and ditches can build up internally in the sediments of the lake bottom. Under certain conditions this phosphorus can be released from the sediment back into the lake potentially fueling algae blooms.
Treatments apply aluminum sulfate (alum) to the lake which binds to phosphorus in the lake, making it unavailable for algae growth. Alum treatments help improve water quality and result in fewer algal blooms and clearer water. For example in graphs above, you can see an improvement in the water quality in 2013 after the first Spring Lake treatment.
Alum treatments are often split into multiple doses. Spring Lake received the final dose of three this year. The first two alum doses were completed in 2013 and 2018. This year marked the first time Upper Prior has been treated with alum. The second and final dose for Upper Prior will be applied in a couple years with the timing determined by lake phosphorus levels.
While alum treatments can be a great tool to bring phosphorus levels under control, they are not a cheap or permanent solution and the sources of external phosphorus entering the lake must be addressed for lasting water quality improvements. As a result, the District’s other projects to reduce incoming phosphorus are very important to the water quality in the long run.
Don’t Forget the Other District Lakes!
The District has roughly a dozen lakes and waterbodies which provide recreation opportunities and habitat for wildlife.
Visit the individual lake pages under the Waterbodies tab for more information about each lake. Water quality data on other District lakes will be forthcoming and posted on individual lake pages on our website once available.
Don’t miss the new Water Quality Report Cards for many of the District lakes including Spring, Prior, Buck, Fish, Cates and Pike Lakes here! Report cards can also be found on the individual website pages for each lake under Waterbodies.
Example Report Card – Cate’s Lake:
