South Dakota lakes dealing with more than just algae and solutions are complicated
MITCHELL, S.D.—With a nearly $20 million cleanup plan currently on the table, it's no secret that Lake Mitchell's algae growth has gotten severe enough to keep the lake from being recreation-friendly.
But although the proposed plan is one of the first of its kind in the area, Lake Mitchell is not an outlier in terms of usability. It may receive more attention than many South Dakota lakes, but it's far from the only lake to have issues with water quality — statistically, it's actually more unusual for a South Dakota lake to not have any water impairments.
With algae blooms becoming such a prominent issue for lakes, especially those in the eastern part of the state, South Dakota State University announced Tuesday, Sept. 18, its faculty and SDSU Extension staff are now working with other professionals in the region to minimize harmful algae blooms.
Lake water quality across the state is so frequently impacted that, according to the South Dakota Department of Environment and Natural Resources' 2018 South Dakota Integrated Report for Surface Water Quality Assessment, just 17.5 percent of all lakes in South Dakota were rated by the Environmental Protection Agency as meeting all of their designated uses. In 2016, that number was 18.6 percent.
In other words, South Dakota lakes are not doing well, and they may very well be getting worse.
Algae blooms across the state
The DENR has identified 575 lakes in South Dakota that have beneficial uses such as recreation or fish life, but that is only a fraction of the total number of lakes in the state.
Of those 575 lakes, the DENR monitors about 30 percent to include in the integrated report.
Paul Lorenzen, an environmental scientist for the DENR who works on the integrated report and specializes in lakes, said it's nearly impossible to say just how many lakes in South Dakota have water quality issues, as typically only those that see much use are chosen to be monitored.
However, of the sampling of lakes that are monitored and included in the integrated report, the issue found in both the most lakes and the most lake acreage in the state is mercury levels in fish tissue, which affects more than 85,000 acres of lakewater in the state. Mercury levels in fish don't affect lakes' recreation potential and are only harmful to people if they eat too much of those fish.
The second-most prevalent stressor in lakewater, affecting 25,678 acres in the state, is chlorophyll-a, which can be related to the algae blooms that hinder Lake Mitchell and 13 other lakes in the James River Basin. That's the main issue that has many South Dakota lakes, especially those on the eastern side of the state, deemed dangerous year after year.
"Out West River, there's probably a little less nutrients in the water there. East River is pretty consistent," Lorenzen said.
Within the James River Basin, which includes Lake Mitchell, the statistics on usability are even lower than the state average. In 2018, just more than 10 percent of DENR-monitored lakes in the basin met all of their designated uses, and just under 29 percent of those lakes have at least one designated use category impaired by chlorophyll-a levels.
The chlorophyll itself, which can be found in pretty much any green, living thing, isn't the issue, but measuring it in a lake can be indicative of an algae problem, which can potentially be dangerous.
"A lot of the algae in a lot of the lakes that we test is what they call cyanobacteria," Lorenzen said. "Cyanobacteria — and I think that's where we might get confused with bacteria and algae — is basically a bacterium, but it's plant-like, so it has chlorophyll. It acts like an algae. For all intents and purposes, we call cyanobacteria algae. And there are certain species of cyanobacteria that can produce toxins that can be harmful to humans."
According to the 2018 Integrated Report, levels of chlorophyll-a and other nutrients are used to determine what is known as a lake's trophic state, which is one of the clearest ways of measuring water quality.
Of the 171 lakes assessed statewide by the DENR for that report, 118 were either eutrophic or hypereutrophic, meaning their levels of these indicators were higher than the norm. A single lake had oligotrophic (less than what is considered the standard) levels of these indicators.
According to the National Lakes Assessment, a report compiled by the EPA, 76 percent of lakes measured in the Temperate Plains — the region of the U.S. that includes the James River Basin — are eutrophic or hypereutrophic. The Northern Plains region, which covers the majority of South Dakota, has a fairly comparable 72 percent. Only areas in the southeastern U.S. have as high a percentage of lakes with excess nutrients.
Searching for solutions
The algae doesn't simply appear in lakes, so solving the problem is more complex than cleaning just the lake itself — something that isn't so simple to begin with.
Mitchell Mayor Bob Everson said that more than half of the nutrients that cause the algae on Lake Mitchell come into the lake from elsewhere in the watershed, which covers 350,000 acres in total.
"I've taken the approach that to do this and do this properly, we need to clean the watershed," Everson said, "and then we need to dredge the bottom of the lake to get rid of the phosphorus in it."
While the rights to many lakes are owned by a nearby city or town — as is the case with Lake Mitchell — the DENR is the state agency that regulates all lakes, as far as water quality.
"DENR is the overall lake police, if you will," Everson said. "Anything we do in the lake, we have to have DENR's approval, and ultimately the EPA's approval."
That means that even if everyone in Mitchell agreed on a cleanup plan, it would still have to be approved by DENR before it could be put into effect.
"If you think about it, it only makes sense, because our lake drains into the Jim River, which hits the Missouri River, which hits the Mississippi River, which ultimately ends up in the Gulf of Mexico," Everson said. "So if we were to create some ecodisaster here, we could have an ecodisaster all the way down to the Gulf of Mexico."