Brown water and red patches in Spring and Upper Prior Lake waters this spring are likely due to a combination of common algae and bacteria, the Prior Lake-Spring Lake Watershed District said Monday.
Brown material was reported emerging from cracks in the ice just before ice out on Spring Lake. After ice out, a brown scum formed on the lake's surface. The scum mixed with water during windy conditions.
Kim Silvernagel, a lakeshore resident of Upper Prior Lake for 19 years, told the district the lake is normally clear this time of year.
Matt Lindon, a Minnesota Pollution Control Agency research scientist, told the district the dominant substance was likely a species of Melosira, a common brown Midwestern diatom. Lindon said he believes the the pink and red patches may have been "colonies of bacteria that can grow under certain conditions."
PLSL Watershed District will continue to collect observations and note conditions, it said in a press release Monday.
"Hopefully this was just a one-time thing, and it will not continue this way for the summer or future years," the statement reads. "If conditions persist, more sampling and analysis will occur."
The district suggested contributing factors could include the severe winter weather, more iron and organic matter in the water column or 2018's fish kill on Spring Lake.