Reports have been made of Blue-Green Algae on Upper Prior Lake this week. Algal blooms are more common in summer months, but they can happen during other times of the year. Please be sure to keep out of the water if you suspect Blue-Green algae as it sometimes contains a toxin that can be harmful if ingested. Pets are especially at risk since they are more likely to go into the water regardless of what it looks like. When in doubt, best keep out!
Steve McComas with Blue Water Science, also known as the “Lake Detective”, stated that he has “seen algal blooms in a number of metro lakes in the last week or two. ” He also connected the recent problems with the weather, the likely culprits being” a combination of the heavy rain, high winds, and warm temperatures, but the algae episode should run its course in a week or two.”
Lakes are usually stratified (separated into layers by water temperature) during summer and winter, but mixing occurs in spring and fall. According to McComas, area lakes are still stratified, but shallow water areas have been mixing. When lakes mix, or “turn-over”, the water from the bottom of the lake comes to the surface, and vice versa. Warm spring air temperatures cause the top of the water to become warmer than the bottom, which in turn causes the lake to “turn over” because of differences in the density of water at different temperatures. Water is most dense at about 39 degrees Fahrenheit. During fall, the cool air temperatures will cool the surface water and create the same phenomena when the surface water becomes cooler than the bottom of the lake. This mixing process can promote algae growth if the bottom of the lake is high in phosphorous and the weather is right. Wind and rain can also cause mixing.
Upper Prior Lake has higher phosphorous levels in the lake bed than both Lower Prior Lake and Spring Lake. The Prior Lake – Spring Lake Watershed District is currently conducting a study to analyze options for reducing the phosphorus in the bottom of Upper Prior Lake. As was done in 2013 on Spring Lake, an Alum treatment is one option being considered. The phosphorous levels are high from an accumulation of many years of input from the watershed. According to studies, most of the phosphorous comes from agricultural areas, but some also comes from urban areas. Urban areas have fertilized lawns and leaves from trees that fall into the streets and are washed into the lake through the storm sewer system. If you live in an area that drains to a lake, some of the things you can do to reduce phosphorous inputs are to use phosphorous-free fertilizers, install native plantings along your shoreline or in a rain garden, mulch or compost leaves and grass clippings, and pick up after your pets.
For more information, please review this past article we posted about Blue-Green Algae if you have algae by your shoreline.