GILLETTE — Paul Langevin first noticed the unusual substance beneath the ice on Keyhole Reservoir in December.

As he’s done for decades, Langevin headed out on the frozen lake to bore a hole and drop a line.

But when he broke through the thick layer of ice, it wasn’t just water that sprang up through the hole.

“It was just so abnormal,” Langevin said about the green substance that emerged from his ice fishing hole. “It was so out of place.”

The 70-year-old Pine Haven resident said he and other ice fishermen who frequented Keyhole State Park this past winter have consistently seen discolored water and strange substances come up through their ice fishing holes, since identified as a harmful cyanobacterial bloom, or blue-green algae.

“Coulter Bay was terrible,” he said. “It was like green pea soup in numerous holes.”

It wasn’t until February that Langevin reached out to Wyoming Game and Fish about the murky substance. He said it was so widely known among ice fishermen this season that he assumed officials also had already known about it.

Once it was finally reported and the reservoir water tested, the Wyoming Department of Environmental Quality confirmed the harmful cyanobacterial bloom (HCB) in Keyhole Reservoir.

“I’ve been ice fishing for 60 years and I’ve never seen that anywhere, anytime,” Langevin said.

He’s not alone.

“We have not seen any prior blooms in the ice or under the ice before and haven’t received any reports to this effect, so this is certainly something new,” said Lindsay Patterson, surface water quality standards coordinator for the Wyoming DEQ, the state agency that tracks those occurrences in Wyoming.

When notified about the substance in the water in late February, Patterson said her department took an initial sample from the lake, but it was not in the area reported and showed fairly low levels of the bacteria.

After conferring with the ice fisherman who reported the algae, a more accurate sample was taken March 8, which found a cyanobacterial density greater than the state’s recreational use threshold.

On March 12, the Wyoming Department of Health issued a recreational use advisory warning of the algae’s presence. The park and the water remains open through the advisory, which will be in place until the bloom dissipates below the state’s threshold of being safe.

“I thought it was such a common problem that everybody that was on the lake was talking about,” Langevin said. “I just assumed the game warden or somebody had brought it to the attention of the biologists. That’s why I never did anything (sooner).”

The Wind Creek area of the reservoir and waters by the dam tested positive for the bacteria, although the park warned on its

Facebook page that there also may be blooms in other parts of Keyhole.

“There are places (on the lake) I don’t go, but every place I have gone I’ve seen it,” Langevin said.

The blooms typically occur when algae begins to grow quickly in the water, usually thriving off of some combination of warm temperatures, still water and nearby nutrient supplies. That also makes the blooms less common in winter conditions, drawing into question how the current bloom came to be, or if it ever went away.

Last summer, the appearance of a similar blue-green algae bloom led to another advisory at Keyhole when the bacteria was reported in August.

At the time, a park patron notified Keyhole staff that a dog became sick and died after playing in the water. The visitor also said she knew of three other dogs that became ill after spending time at Keyhole, Wyoming State Parks Deputy Director Nick Neylon said last summer.

The advisory stayed in place through the late summer season and had dissipated by the end of September, but it is unclear if the algae itself ever left the reservoir.

There are several conditions that cause the blue-green algae to grow, although how they combine to create a bloom is still not fully understood.

To grow, Patterson said the cyanobacteria needs nutrients, or a food supply, like nitrogen and phosphorus that can often come from the surrounding landscape.

She said the microscopic bacteria tend to out-compete other organisms at higher temperatures and that still water can further help the bacteria, with its self-regulating buoyancy, to grow and spread.

However, in the case of the anomalous bloom at Keyhole this winter, it is unclear how it formed under the ice, or if it even may have never gone away from last summer.

Last year, the recreational use advisories statewide were in effect until the blooms dissipated or until Sept. 30. But it is unclear if all of the reported blooms had cleared by then.

“We didn’t really have hard data on whether the bloom entirely dissipated or not,” Patterson said.

By the end of summer, tracking each of the algae blooms throughout Wyoming can become challenging with the staff the DEQ has to work with, she said.

“It’s certainly possible that it just persisted through the fall,” she said.

Since the department began tracking blooms, Patterson said the number of reported occurrences has gone up each year. But she said it is difficult to tell if it is a product of people on the lookout for it more or if the blooms are actually happening more frequently.

Henderson, who has been at Keyhole for about a year, said that staff who have been there for longer than he also don’t recall seeing a winter algae occurrence like this before.

“The people who have been here at Keyhole for 10, 15 years, none of them seem to know of it ever happening before,” Henderson said. “We weren’t sure if it just wasn’t happening or it wasn’t being reported.”

The DEQ still has tests to run on the Keyhole samples to determine how toxic the blooms may be.

“That will tell us whether the bloom is actually releasing toxins,” Patterson said.

Those results likely won’t be known for weeks. Still, even at varying levels of toxicity, the blooms can have harmful effects on people and animals, she said.

“The implications are if the cyanobacteria are producing toxins, it’s something for the public to be aware of,” Patterson said. “It raises the potential risk associated with the bloom.”

With ice still covering a significant part of the reservoir, it is difficult to pinpoint precisely where the algae is distributed and which areas it’s most dense, she said.

Langevin said he has seen it in every part of the lake he has fished, noting that he has not fished the entire body of water.

While the bloom was most commonly green when it appeared through the ice, he said that he has seen black substances come through some of his fishing holes as well.

“The cyanobacterial bloom that we’ve had the past two years in late summer, all anybody’s ever said is as soon as the lake gets cold it will disappear,” Langevin said. “This year, it seems to be thriving under the ice in the cold water.”

Through mid-March, Henderson said there are patches of the lake with 10 to 12 inches of ice and other patches with open water, making the prospect of ice fishing at this point in the season a little “sketchy.”

Even with the advisory in place last year, he said no sections of the lake had to be closed.

The ice on top of the lake makes it more difficult to visibly gauge where exactly the blooms are or in which parts they’re more dense.

The algae is not something that can just be whisked away. While posted signage and parks workers can warn people to avoid it, they can’t just scoop it out of the lake themselves.

“These are naturally occurring organisms in the reservoir,” Patterson said. “It’s not something that’s been introduced. … It’s just in some instances, the conditions can be just right for them to proliferate and take over.”

Although the park is still open to the public with the blue-green algae present, the advisory recommends taking precautions.

Avoid water in the area of the blooms, especially where it can be seen densely. Be careful of ingesting the water. Boiling, filtering or otherwise treating the water will not remove the toxins, according to the recreational use advisory.

With the lake remaining cold and iced over, swimming is less of a concern now, but may be an increased risk if the bloom persists into the summer.

Animals are especially at risk and should avoid the water near the blooms. If they do come into contact with the algae or nearby water, rinse them off and contact a veterinarian, the advisory warns.

People can still fish at Keyhole, but Henderson said to be careful with handling and eating their catches.

“We’re just letting people know that we do have the blooms out here,” Henderson said. “If you do fish, make sure you’re rinsing your fish. Eat the fillet portion only, don’t eat any of the skin.”

Despite the murky water, Langevin said he still carefully cleaned and ate the fish he caught at Keyhole this year without issue.

With the occurrence of the blooms being relatively recent and growing in incidence, Patterson advised that “if folks see things they think are out of the ordinary, (they should) do their best to report them.”

The mystery of when the bloom formed, what caused it or when it will leave is about as clear as the algae-covered patches of lake at Keyhole. But for now, it stands as a unique occurrence in northeast Wyoming wildlife that has raised more questions than answers.

“It will be interesting to see if this happens again in the future or if this is an anomalous event,” Patterson said.