A ‘C’ ranking for the Minneapolis Chain of Lakes is a triumph of environmental restoration

The summer clouds over Cedar Lake in Minneapolis looked like they could go either way. A pair of kayakers getting ready to launch smiled at the mist in the air and decided to chance the rain. Nearby, a fisherman leaned against a tree and cast. Behind him, an old yellow Lab pulled its owner down a walking path that circled the lake. A steady stream of joggers followed, and cyclists, who shouted “on your left,” with the backdrop of the Minneapolis skyline.

The most visited slice of nature in Minnesota isn’t in a state or national park. It’s not an old-growth forest or patch of surviving prairie. It’s the chain of four lakes that starts with Cedar and ends with Lake Harriet in the heart of Minneapolis.

Until about 30 years ago, the Chain of Lakes seemed like it would be lost, to be slowly strangled by all the pollution and runoff of the metropolis that grew up around it. A forward-thinking project that started then — the largest of its kind at the time in U.S. history — reversed decades of environmental degradation. The benefits of that work continue today.

“Those investments occurred at a great time to make sure these lakes didn’t reach a tipping point,” said Michael Hayman, the director of project planning for the Minnehaha Creek Watershed District. “And they’ve been very stable ever since.”

The Minnesota Department of Natural Resources started issuing grades and scores to about 3,000 lakes in 2023. The grades, for the first time, give residents and local governments an easy to way to look up the condition of their lake and compare it to others without needing to scour through reams of pollution data. A searchable database of every lake with a grade was built by the DNR’s Watershed Health Assessment Framework program.

The letter grade, from A+ to F — based on a 0 to 100 score — denotes the health of a lake and how far it has fallen from what a lake of its size, depth and region should be. A lake’s score is based on how polluted it is, whether fish and native plants survive, and the development on its shoreline and watershed.

There are 11,842 lakes in Minnesota, many of which are too remote or small to have been consistently studied. Biologists scored every lake that has enough data, which tended to be the biggest and most popular. Lake Superior, Lake of the Woods and other border lakes were omitted.

The four lakes in the Minneapolis chain — Cedar, Lake of the Isles, Bde Maka Ska and Harriet — were all given C’s. In some parts of the state, more wooded and natural than Minneapolis, a C could be cause for alarm. For a series of lakes that collect all the stormwater from tens of thousands of homes and businesses, and hundreds of miles of some of the busiest roads in the state, the scores are remarkable. They highlight a sharp turnaround from when the chain was at a crisis point.

By the 1990s, the lakes were in bad condition and getting worse. The marshes, woods and prairies that once surrounded the chain had long been drained away and paved. Native plants were dying off, likely because sunlight wasn’t penetrating the murky water, said Rachael Crabb, the water resources supervisor for the Minneapolis Park Board. Water clarity was declining. Algae blooms were frequent.

Citizens urged the city to take action, writing in the Star Tribune that Brownie Lake, which flows into Cedar, was “indeed on its deathbed — less a living environment than a chemical sink.” On Cedar Lake, citizens complained of “turbidity, ammonia smells, fish kills and swimmer’s itch.”

Unless major changes were made, experts warned, the water would continue to get worse and the lakes would end up on the state’s infamous impaired waters list. In a matter of years, the chain could be overrun by nutrients and bacteria to the point where it would be unsafe to swim. Large numbers of fish and other aquatic life would die off.

The main culprit, as it often is in fresh water, was phosphorus.

With every wetland drained and home, parking lot and street built, Minnesotans were shooting more and more phosphorus into the Chain of Lakes. Algae and cyanobacteria were taking full advantage.

A Minnesota Pollution Control Agency report found that Cedar Lake, the first in the chain, had nearly three times the phosphorus it had before development. Along with that phosphorus, a toxic stew of pet waste, fertilizers, pesticides, chemicals and oils was piped directly into the lakes from lawns and streets through stormwater systems.

While the lakes are inside Minneapolis city boundaries, much of the land that drains into the lakes is outside the city’s jurisdiction.

It was immediately clear that Minneapolis would not be able to fix the problem alone. Spurred on by citizens, the city formed a Clean Water Partnership with several agencies and organizations including the Minneapolis Park and Recreation Board, St. Louis Park, Edina and the Minnehaha Creek Watershed District.

They divided up the $12.4 million cost of the restoration project and started work in 1995. First, they found the key areas where much of the pollution was entering the chain, which happened to be on parkland already publicly owned.

In St. Louis Park, the partners dredged out phosphorus-laden silt from the bottom of Twin Lakes, a small lake upstream of the chain. They also dug out a small pond just upstream of Twin Lakes, to help settle out nutrients and pollution.

On Bde Maka Ska, the group excavated three ponds that function as a wetland near the southwest shore. The ponds allow the nutrient- and chemical-laden water entering the lake to settle, leaving toxins and phosphorus behind while cleaner water passed through.

The city also increased its street sweeping program and started a public education campaign to cut down on the pesticides, grass trimmings and fallen leaves washing into the lakes. As grass and leaves decompose in water, they feed bacteria and algae that remove oxygen, suffocating fish. Grit chambers were added to stormwater pipes to create choke points that slow down the incoming water, allowing the nutrients and trash to settle into a black sludge. The sludge is eventually vacuumed away and taken to a landfill.

Once the incoming tide of pollutants was dealt with, the partnership went about getting rid of the excess phosphorus that had built up in the lakes over the decades. They did it by spraying alum over the water. Alum binds to dissolved phosphorus as it sinks, taking the nutrient out of the water column and planting it firmly on the bottom of the lake, where algae and bacteria cannot feed off it.

The results were rapid.

Many restoration projects are successes if they can stop 10 or 20 pounds of phosphorus from entering a lake. The Environmental Protection Agency estimates the work in the 1990s has been stopping 600 pounds from entering the chain every year since.

The lakes have needed periodic work since the project finished. The Watershed District has spent about $500,000 regularly dredging the ponds and wetlands that were installed. It also spends about $35,000 a year maintaining vegetation along the shores. The Park Board has received a little more than $8 million from the state’s Outdoor Heritage Fund since 2010 to install paths and fishing docks and to stabilize the chain’s shorelines.

The Park Board also chips in about $450,000 a year to help the city maintain, design and improve its stormwater infrastructure and street sweeping program to keep nutrients and trash out of Minneapolis lakes.

The lakes still have their problems. Beaches close periodically because of E. coli or blue-green algae outbreaks. Sodium from road salt has been threatening urban lakes in Minnesota for the past 20 years. The chain remains in a watershed that has been almost entirely developed and paved.

That development, and the high stormwater flow that results, puts stress on fish and habitat that is difficult to reverse, Crabb said.

“Our parkland area is so small compared to undeveloped land around outstate lakes,” Crabb said. “All Minneapolis lakes score lower on biodiversity and species richness and habitat quality portions of the metric. That’s not unexpected for lakes within 15 minutes of a major cities’ downtown and habitats that receive large stormwater inputs.”

As winters get warmer, the lakes have less ice coverage, which has lengthened the growing season for bacteria and plants. Blue-green algae blooms, which often look like bright-green pea soup and can kill dogs, are increasing, at least partly due to the longer growing season, Crabb said.

But on a Saturday morning in July, none of those problems was evident as the rain held off and the sun peeked out over Bde Maka Ska. The paths were busy with dozens of joggers, while picnic benches were filled under the shade of old oak trees. Four sailboats slowly circled the deep waters. Under a fishing pier, small bluegill lazily swam in the shallow, clear water.

A pair of spiny softshell turtles crawled from the water onto the sand of one of the beaches. A man trying to take a picture scared them, and they sprinted back into the water faster than one might think a turtle could. The man left, and one of the turtles watching from the water crawled back out to the beach and rested in the sun, as though it decided that while the lake may be a little crowded, all in all, everything was OK.