The results from the Spring Lake alum treatment (featured in the November 9^th edition of the Prior Lake American) are looking good, according to water quality data released by Barr Engineering.

Before the treatment started, Barr Engineering collected water samples from Spring Lake and measured total phosphorus and Chlorophyll-A.  Monitoring chlorophyll levels is a way to track algae blooms. Surface waters with lots of algae are typically high in nutrients, like phosphorus and nitrogen; that’s why it’s also important to measure phosphorus, because phosphorus drives algal growth. For reference, lakes like Spring are not supposed to exceed 40 micrograms per liter (µg/L) for total phosphorus and 14 µg/L for Chlorophyll-A in Minnesota.

Prior to the treatment, Barr recorded 220 µg/L of total phosphorus and 45.5 µg/L of Chlorophyll-A for Spring Lake. On November 1^st, following the alum treatment, Barr measured 59 µg/L of total phosphorus and Chlorophyll-A concentrations of 4 µg/L, which indicate a significant drop in phosphorus and chlorophyll concentrations. While these initial results are positive, the real test will come next spring when the lake has to compete with spring runoff and warming temperatures.

PLSLWD staff will continue monitoring Spring Lake in the spring once conditions allow, since our monitoring program has wrapped up for the season. We have a long way to go to clean up Spring Lake, but it looks like this big first step went well.

HAB Aquatic Solutions, Inc. finished dosing Spring Lake with alum on November 1st. The crew only encountered a few windy days during the course of the treatment, but were able to successfully navigate toward the sheltered side of the lake to continue dosing without delay.

Below you can check out the before and after pictures taken from the wheelhouse on the barge. During the application, as the alum settles toward the lake bottom it sweeps phosphorus out of the water column, and the impact is quite clear!

Before:

First Day on Spring Lake

After:

Final Day on Spring Lake

As you can see, there’s quite a difference!

On the last day of the treatment, Barr Engineering recorded a significant (almost one meter) improvement in water transparency. District staff will continue monitoring in the spring once conditions allow, since our fall monitoring has wrapped up for the season. We have a long way to go to clean up Spring Lake, but it looks like this big first step went well.