Seeking Clarity on Lake Restoration

Minnesota: the land of 14,380 lakes. Minnesotans care deeply about their lakes, whether it be for swimming, fishing, or enjoying a picnic on the lakeshore. When I picture a perfect day on the lake, I think about warm sun, soft sand, and clear waters. Imagine my dismay when instead of clear waters, I’m met with thick blooms of bright green, foul smelling, and potentially toxic algae. Luckily, Minnesotans are dedicated to getting our perfect beach days back. Sixty-four lakes have been successfully restored over the last 20 years, 44 of which are in the Twin Cities Metropolitan Area (TCMA). As a PhD student in the MSP LTER, my research focuses on how reducing nutrient pollution affects the entire lake ecosystem.

What Makes a Shallow Lake Murky or Clear?

Algal blooms are driven by nutrient pollution, specifically excess nitrogen and phosphorus. Actions like separating the sewage and stormwater systems, a phosphorus fertilizer ban, and more street sweeping have decreased the amount of nutrient pollution entering TCMA lakes. Despite this, many lakes are still too rich in nutrients, and phosphorus has created a particularly sticky problem. Instead of flushing out of the lake, phosphorus sticks to the muck at the bottom of the lake. This means that phosphorus pollution from decades ago may still affect lakes today. In the summer, that legacy phosphorus leaches into the water, fueling algal blooms. If muck at the bottom of the lake gets stirred up from common carp feeding, boat motors, or heavy storms, the problem gets even worse.

Shallow lakes have a natural defense against murky water: aquatic plants. Shallow lakes often look one of two ways: clear and full of underwater plants, or murky and full of algae. While algae takes most of the blame for poor water quality, aquatic plants (often called “weeds”) don’t have a great reputation either. They feel slimy against your skin when you’re swimming and get tangled in boat propellers.

However, aquatic plants are critical to keeping shallow lakes clear. Their roots stabilize the lake bed, preventing phosphorus-rich muck from being churned up into the water. They also capture nutrients that might overwise fuel algal blooms.

What Are We Doing to Address This Problem?

Transformative lake research often occurs at research stations where experiments are conducted on entire lakes, like at the Experimental Lakes Area in Canada where the link between phosphorus and algal blooms was demonstrated in the 1970s. To me, the TCMA is our own experimental lakes area, where local lake managers conduct whole-lake experiments every year in the form of evidence-based restoration practices. Researchers in past decades focused on what happens when nutrients are added to lakes, simulating pollution. Through the MSP LTER, we get to learn what happens when nutrients are removed. Do algal blooms go away? Do aquatic plants recover? Even as we reduce pollution, are new threats like wake boats or invasive species endangering the progress we’ve made?

Two ways lake managers have successfully reduced the impact of legacy phosphorus are alum treatments and carp removals. Over 100 alum treatments have occurred in the TCMA, chemically binding phosphorus and keeping it out of the water. Since 2022, my research has brought evidence from these treatments together to understand what happens when lakes suddenly have less phosphorus. Sometimes plants recover, sometimes they don’t, and sometimes plant growth takes off to the point where the lake becomes impassable. Plant growth may increase  the effectiveness of alum treatments by stabilizing the lake bed and sucking up both nitrogen and phosphorus.

In 2024, University of Minnesota researchers partnered with local lake managers to study the effects of common carp removal through the Lab to Lakes initiative. I’m excited to continue my research through this collaboration to learn if lakes respond differently to carp removals compared to alum treatments.

Achieving Clarity

Sometimes being a scientist feels a lot like being a shallow lake; your ideas feel really murky at the beginning, but with time and effort you can find clarity. From 2023 to 2025, I watched a small lake in Eagan shift from murky and green to clear and full of plants thanks to an alum treatment and carp removal. What was once a lake where I didn’t even want to touch the water is now full of native plants and great for catching sunfish. In a similar way, our picture of how management restores lakes also grows clearer. With continued collaborations between researchers and lake managers, there should be many more perfect beach days to come.