Blooms at reservoirs, lakes caused by nitrogen and phosphorus


RAWLINS – It might look like grass clippings, blue-green scum or spilled paint on the water surface. It might be suspended in the water or attached to rocks, sediments and plants. It might be a harmful cyanobacterial bloom.

In mid-July, the Wyoming Department of Health issued a recreational use advisory for Seminoe Reservoir in Carbon County due to a harmful cyanobacterial bloom (HCB), commonly known as blue-green algae. 

Seminoe is the only lake under a current advisory as of Friday morning, but reports of HCBs at Saratoga Lake, Boysen Reservoir, Ocean Lake, Leazenby Lake, Woodruff Narrows Reservoir and Wheatland Reservoir #3 are under investigation.

The Department of Health started issuing advisories for HCBs in 2017 when the Wyoming Department of Environmental Quality received reports of blooms at a few reservoirs, according to Lindsay Patterson with the DEQ. Since 2017, there has been an increase in public reporting, likely due to an increase in awareness, she said. In addition, DEQ has started to look for blooms by using satellite imagery.

“As a result, there has been an increase in the number of blooms DEQ investigates per summer, and a corresponding increase in the number of advisories issued,” Patterson said. “To date, we have not evaluated whether the prevalence of blooms has increased in Wyoming, however, there are some studies that suggest that the number of blooms are increasing at the national and global scale.”

DEQ uses satellite imagery to identify cyanobacteria because of their unique spectral signature; however, lakes and reservoirs have to be a sufficient size for the satellites to accurately detect cyanobacterial blooms, she said. Satellite imagery is generally used for the 40 largest lakes and reservoirs in the state.

Reports from the public and waterbody management on site, she said, are crucial on smaller bodies of water.

Cyanobacteria and the toxins they may produce can cause serious illnesses in people and animals. 

The Wyoming Harmful Cyanobacterial Bloom program is a partnership between DEQ, the Wyoming Department of Health, the Wyoming Livestock Board and local, state and federal resource management agencies, with the goal of informing the public about blooms to minimize exposure and prevent illnesses.

Cyanobacterial blooms are most commonly caused by excessive amounts of nitrogen and phosphorus from fertilizers, animal waste from pets and livestock, wastewater from treatment plants and septic systems, detergents, stormwater runoff, cars and fuel-burning power plants. In addition, wind, shallow water with abundant sunlight, warm temperatures and still or slow moving water can contribute to bloom formation.

“Since we have less control over water temperatures and wind, DEQ recommends people try to minimize the amount of nutrients reaching our surface waters,” Patterson said. “Use appropriate amounts of fertilizers, use phosphorus-free detergents, properly maintain septic-systems, pick up pet waste and minimize or treat runoff from agricultural fields and urban areas.”

Dr. Karl Musgrave, state public health veterinarian and environmental health epidemiologist with WDH, said that for a person or animal to be significantly impacted by the blooms, the bacteria must be ingested.

“It is a toxin, so you have to ingest it. Dogs are the main problem, because they jump in the water and drink a lot when they swim around,” Musgrave said. “People that go to the lake and don’t ingest the water don’t have too much of a problem. They can get a rash from wading in the water … but you really have to ingest the water to have serious health problems.”

Because cyanobacteria prefer warmer conditions, most blooms begin to disappear once the air and water cools in the late fall and winter, according to Patterson.

“That being said, there have been reports outside of Wyoming that some species of cyanobacteria may persist during colder conditions and under ice,” she said.

DEQ does not have data to determine whether cold-weather blooms occur in Wyoming, and so recommends the public be vigilant of blooms in all seasons, avoiding green water, floating scums or mats and the appearance of paste on the shoreline.

Sara DiRienzo, public information officer with the Wyoming Game and Fish Department, said that while her agency is not directly involved with the public information campaign or tracking efforts, they are aware of the blooms and work alongside DEQ and the WDH because people use affected bodies of water for recreation.

As to whether the blooms have any effects on wildlife, DiRienzo said it may depend on the bloom. Fishermen are advised to rinse fish with clean water and eat only the fillet portion.

“The bloom can have an impact on animals if they consume the water, but it is pretty rare,” DiRienzo said.

The blooms are different than aquatic invasive species, which can spread when species become attached to a boat or survive in water carried on boats from one water to another.

“Aquatic invasive species are an organism that is not native to our state or our state’s water, and those are typically brought in by boaters,” she explained. “There is not too much of a connection between the two, but … boaters are helpful in both cases because sometimes recreationalists and boaters are the ones out in the water and are the ones who spot a bloom and they can help by reporting that.

Boaters have a role in keeping aquatic invasive species out of Wyoming by stopping at check stations, undergoing inspection, and cleaning, draining and drying all of their boating equipment.

“That is the number one way we can prevent aquatic invasive species getting into our water sources,” DiRienzo said “Boaters play a huge role in keeping an eye out for blooms, and also taking an active role in preventing the spread of aquatic invasive species.”

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