A colony of cormorants is dumping 14,500 pounds of feces in this south metro lake

The murky mocha-colored water in Lake Augusta is as off-putting as the source of its pollution: bird droppings, lots of them.

Every fall, thousands of migrating double-crested cormorants roost in the dead trees ringing the Mendota Heights lake and defecate, dumping roughly 14,500 pounds of phosphorus-rich feces into the water — and creating an intractable environmental problem for their human neighbors.

“It’s like the movie ‘The Birds,’” said neighbor Barbara Kaufmann, jokingly comparing the annual swarm of black-feathered cormorants to the 1963 Hitchcock film.

Kaufmann is one of several Augusta Shores residents focused on cleaning up the lake, which landed on the state’s impaired waters list in 2010. The roughly 700 dead trees that jut from its mucky waters have become a magnet for cormorants that deposit pollutants into a body of water lacking a natural outlet.

But in this man vs. bird fight, it appears the feathered camp might have the advantage.

The lake’s waters have risen 15 feet since 1984, creating a cycle of contamination as trees rapidly die and attract a broadening flock of birds whose feces spawns algae blooms. Conservation groups working with the residents have rejected using sharpshooters to cull the cormorants, a native species protected by the federal Migratory Bird Treaty Act.

Experts say the birds will swiftly adapt to loud bangs, strobe lights and other methods to deter them from the area. They worry, also, that messing with the population could prove disastrous should the colony migrate west toward the airport and collide with planes.

And then there are those who want to preserve the unconventional “conservation area” that Lake Augusta has become.

“It’s a very unique situation,” said Joe Barten, an administrator at the Lower Mississippi River Watershed Management Organization. “There’s no silver bullet to fix lakes, and especially not this one.”

The 44-acre Lake Augusta curves around a private community of manicured lawns and large houses called Augusta Shores. Part of the shore abuts a Catholic cemetery.

The greenish brown expanse — unmistakable from planes due to its unappetizing hue, residents say — wasn’t always that way.

Neighbor Joe Nuñez said Minnesota governors reportedly fished on the public waters a century ago, kids swam in it 30 years ago and these days it draws a handful of ice anglers in the winter. (Barten said scientists believe the water is inhospitable to fish.)

“With climate change and the excess rain that we’ve had over the last decade, water level has risen substantially,” Mendota Heights public works director Ryan Ruzek said.

In 2017, the watershed organization and Mendota Heights began treating the lake with alum to reduce contaminants, including phosphorus. But after early signs of progress, phosphorus levels rebounded.

The churning of buried sediment that’s packed with bird poop, stormwater runoff and phosphorous-tinged rainfall all add to the lake’s contaminant levels, Barten said.

But the birds, which fish in the river valley during the day and roost around the lake at night, play an outsize role, with their feces accounting for about one-third of the lake’s total phosphorus over the last decade on average. In a dry year like 2022, their excrement was responsible for 68% of all the phosphorus in the water.

“The habitat has just been super conducive [to] the birds,” Barten said.

The state has occasionally cracked down on cormorants, which one University of Minnesota researcher once dubbed the “most hated bird in the world” for their inelegant appearance, a bit like a cross of a goose with a crow.

U.S. Department of Agriculture sharpshooters have killed thousands of cormorants that feast on yellow perch at Leech Lake in north central Minnesota.

A federal judge in 2016 ended the open-ended, lethal culling of cormorants, once endangered in some states. Since then, Minnesota cities have occasionally obtained permits from the U.S. Fish and Wildlife Service to shoot the birds in limited circumstances.

Gail Fraser, an ecology professor at York University who studies a 16,000-bird colony of cormorants in Toronto, said that although cormorant feces is a well-established threat to tree health, the birds are responding to a landscape that humans have profoundly altered.

Management efforts often “move the problem down the road,” Fraser said, noting that efforts to stop the birds from nesting along a river in the Pacific Northwest pushed the colony to take shelter on a bridge connecting Oregon and Washington.

Experts worry the Mendota Heights cormorants will move to a nearby lake or land near the airport if they deploy “harassment” techniques to scatter the birds, like fireworks, lasers and dogs.

So officials and residents have coalesced around solutions outlined in a 2023 study that Mendota Heights and the watershed organization commissioned.

Those ideas include installing an outlet to flush the phosphorus-rich feces and reduce water levels, treating stormwater runoff before it spills into Lake Augusta, stabilizing the shoreline and removing dead trees to discourage cormorants from roosting.

But someone would have to pay for it.

Ruzek, the city public works director, said the city could pursue grants and state bonds, plus assess residents living along the lakeshore, to fund the improvements.

“The city wouldn’t have the funds,” he said.

Barten recommends additional study of the birds’ behavior before taking drastic action. But that, too, could saddle the city or residents with a steep bill.

The residents, meanwhile, will watch the lake continue to rise, its water growing ever cloudier, knowing the cormorants will come again in the fall.

“Doing nothing isn’t a solution,” Nuñez said. “And it’s getting worse.”