When the summer sun shines and temperatures begin to rise, conditions become ripe for Minnesota lakes, especially in the southern portion of the state, to produce algal blooms and give the waters a recognizable green tinge. This is quite common in late summer and occurs in waters such as Split Rock Creek State Park and Split Rock Creek.
Algae (i.e., phytoplankton) are microscopic aquatic plants and are a natural part of any aquatic environment, and they play a critical role in aquatic ecosystems according to information from the Minnesota Pollution Control Agency (MPCA).
“We are in the time of year when algae blooms are common,” said Skip Wright, regional hydrologist with the Minnesota Department of Natural Resources (MNDNR).
Information taken from the MNDNR Web site states that algal blooms are generally recognized by a change in water color. For example, severe blooms often resemble pea soup, whereas blue-green algae forms unsightly, jellylike masses or a blue, paint-like scum on beaches and shorelines.
According to the MPCA, Minnesota’s lakes and streams support numerous varieties of algae, and most are harmless. However, under certain conditions some algae species can be harmful.
“The most common type of algae in this area is blue-green algae,” said Chuck Obler, fisheries technician with the MNDNR in Windom. The Windom office covers a 10-county area in southwestern Minnesota that includes 100 lakes.
Obler said it is hard to tell which lake will have an algal bloom and which won’t, or when they’ll bloom.
“It varies from year to year,” he said. “There doesn’t seem to be any rhyme or reason other than lakes in the southern part of Minnesota are more susceptible because the lakes are warm and shallow, with high nutrient levels, making them more fertile.”
Information from the MPCA says there is no single factor that causes an algal bloom. A combination of factors such as excessive nutrients, warm temperatures, and lots of sunlight all encourage the growth of blue-green algae. A primary cause, excess nutrients (e.g. phosphorus), is largely due to nonpoint source runoff from agricultural lands, urban areas, and point sources such as wastewater treatment facilities.
There are many different species of blue-green algae but the MNDNR says some of the more common include Anabaena sp., Aphanizomenon sp., Mocrocystis sp., and Planktothrix sp,. It is not always the same species that blooms in a given waterbody, and the dominant species present can change over the course of the season.
These are generally harmless, but according to the MNDNR when some species of blue-green algae are decaying, their cells release toxic materials, which can poison animals that drink the water.
“Typically we only have one or two of these a year or every other year,” Obler said. “We currently have a lake in Martin County where we have some fish kill.”
The bloom is so thick it cuts out sunlight and uses up the oxygen in the lake, thus causing the fish to die.
In cases where fish kills occur, the MNDNR will test oxygen levels in the water, Obler said.
“Blooms are usually worse in late-July, early August,” he said. “The algae usually dies off when water temps get cooler or even from a cool rain. Some may last from late-July until freeze up. But each lake is an individual case on how long it will last.”
Obler says that there are no quick or easy remedies for the control of blue-green algae once they appear in a lake or pond. But by reducing the amount of nutrients that wash into lakes and ponds it will eventually reduce the frequency and intensity of blue-green algal blooms.
He also pointed out that there are management practices for lakes and streams to help prevent algal blooms from occurring such as cleaning up the inlets leading into the lake or planting buffer strips to help keep nutrients from entering the lake or pond.
“Some lakes have had success using copper sulfate to control algae levels,” Obler said. “But this is typically a band-aid approach to the problem and doesn’t treat the cause.”
