A cyanobacteria bloom found at Leazenby Lake, also known as Hundred Springs Reservoir, July 15, 2021. The dominant cyanobacteria taxon found in this bloom is Phormidium. (Wyoming Department of Environmental Quality)

It can look like green paint spilled on the surface of a lake. Or like cottage cheese. Or grass clippings. 

Many people call it blue-green algae, even though on the tree of life, cyanobacteria is pretty far away from algae. 

As summer reaches its late stage, chances are good that Wyoming residents have noticed it. Dangerous blooms tend to infest waterways in  mid-to-late summer and can emit toxins strong enough to kill dogs and even cows. 

“Cyanobacteria occur naturally at low levels in aquatic ecosystems, but they can proliferate under ideal conditions — meaning often when temperatures are elevated, when there is still or slow-moving water or when there is elevated nutrient concentration,” said Lindsay Patterson, surface water quality standards supervisor for the Wyoming Department of Environmental Quality. “The wind can also aggregate them in portions of water bodies.”

Health alerts about cyanobacteria blooms also proliferated across the state this summer, from Brooks Lake and Pelham Lake in the Shoshone National Forest to Boysen Reservoir in central Wyoming to Sloans Lake in Cheyenne, leading many recreationists and even researchers to wonder: Are these blooms getting worse?

The long answer is complicated. The short one is: maybe. 

“The more people become familiar with the topic and health risks, we hear about them more and we are actively looking for them more,” Patterson said. “I wouldn’t say they are increasing necessarily, but it’s hard to tease it apart.”

Increasing awareness 

Cyanobacteria evolved about 3 billion years ago. Not all emit toxins, and most cyanobacteria at low levels aren’t harmful. It’s when concentrations elevate that problems begin.

A cyanobacteria bloom at Wheatland Reservoir #3 on Aug. 24, 2021. (Wyoming Department of Environmental Quality)

Toxic blooms form for a variety of reasons, including warm weather and stagnant water. While they’re most often associated with lower-elevation reservoirs and places where nutrient runoff from agriculture, fertilizers, urban areas, wastewater treatment plants, oil and gas facilities or septic systems is high, they don’t exclusively form in areas with direct runoff. For reasons researchers are still trying to parse, the U.S. Forest Service is discovering more of them in high-mountain lakes, which could be attributed to atmospheric pollution or cycling of nutrients from forest fires or even beetle-kill trees. 

It wasn’t until about 2014 when the state (and nation) began to take cyanobacteria blooms more seriously. The city of Toledo, Ohio found high enough levels of toxins in Lake Erie from a cyanobacteria bloom that officials shut off water for about 400,000 people

“There’s been a much more concerted effort since then to study these and figure out how prevalent they are,” Patterson said. 

In Wyoming, that effort involves satellite monitoring of 40 of the state’s lakes and reservoirs. The satellite scans each body of water, and images are processed by the Cyanobacteria Assessment Network, a conglomerate of federal agencies. Kelsee Hurshman, natural resource analyst for Wyoming DEQ, then uses those processed images to track the blooms’ evolution throughout the summer. 

The effort is turning up more and more blooms. Once it’s verified that there are elevated densities of cyanobacteria, the Wyoming Department of Health alerts the public. 

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Cyanobacteria toxins, in high quantities, can be strong enough to kill a cow if it drinks the water containing the bloom. They can also kill dogs and cause irritation on human skin. Health advisories ask people not to swim in areas with blooms, and to carefully fillet any fish caught in places with blooms and throw away the skin.

According to The Environmental Protection Agency, “Although there are relatively few documented cases of severe human health effects, exposure to cyanobacteria or their toxins may produce allergic reactions such as skin rashes, eye irritations, respiratory symptoms and in some cases gastroenteritis, liver and kidney failure or death.”

A future of blooms?

Once a bloom forms, it doesn’t typically dissipate until late fall in Wyoming when lake temperatures drop enough to kill off many of the cells, which then sink to the bottom and are consumed by microbes.

While Patterson isn’t sure if blooms are increasing or not, warming temperatures caused by climate change certainly aren’t helping, she said. And, she added, late-summer blooms and health department cautionary notices are likely to increase in the future as long as monitoring continues. 

That’s partly why research is so crucial, Patterson said.

An aphanizomenon cyanobacterial bloom at Woodruff Narrows Reservoir on July 27, 2021. (Wyoming Department of Environmental Quality)

Sarah Collins, an assistant professor of zoology and physiology at the University of Wyoming, is leading a project that compares those satellite images to what exists on the ground. The team is also developing genomic techniques to identify which types of cyanobacteria are responsible for blooms and how many toxins they produce. 

Once some of that information is better established, researchers and water managers can begin to talk about solutions. 

Smaller, private ponds have a few easier potential fixes, Patterson said. Landowners can line the banks of the lake or pond with barley straw, she said, which seems to deter the blooms from forming. 

Aerators also can help by forcing the water to move and not allowing blooms to form. 

Neither of those are exactly practical on a reservoir the size of Boysen or Flaming Gorge, however. 

Limiting nutrient pollution discharges could also help, though Patterson cautioned that cutting back on pollution won’t solve all of the blooms. 

“I don’t want to lead anyone astray and say if we take care of the nutrients, it will 100% address the problem,” Patterson said. “It will certainly help, and is one thing we can work on through regulating some point-source discharges and working with nonpoint discharges to keep nutrients on the ground or out of waterways.”

Patterson also reminds people that just because a body of water has an advisory doesn’t mean the entire thing is dangerous. The bloom could be located in one arm of a lake where water stays stagnant and warm. Other parts of the lake could be fine.

“We don’t want to deter everybody from recreating,” Patterson said. “Certain activities are less risky than others. If you’re fishing or in a boat and not coming into a lot of contact with a bloom, the risks are reduced.” 

A cyanobacteria bloom on Aug. 24, 2021 at Rainbow Lake. The dominant cyanobacteria in this bloom are Aphanizomenon and Dolichospermum. (Shoshone National Forest/Wyoming Department of Environmental Quality)


For more information on toxic cyanobacteria or to report a possible bloom, go to wyohcbs.org. For more information on the effects on human health, go to health.wyo.gov.

Christine Peterson has covered science, the environment and outdoor recreation in Wyoming for more than a decade for various publications including the Casper Star-Tribune, National Geographic and Outdoor...

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  1. Using technology and recording information about the blooms is all well and good. That should have begun decades ago, though.

    My anecdotal observations at Boysen Reservoir over the last 20 years suggest that the algae blooms have in fact increased, particularly over the last couple of years. I used to let my Lab swim regularly in the reservoir, but I keep him away now, because the blooms have increased, particularly in the coves, and I don’t want to do anything that might negatively affect his health.

    As usual, Wyoming guvamint waits until it is far too late to do anything. Next, they’ll probably be telling us that disposing of fracking chemicals into streams feeding into reservoirs is good because it might control the algae. Talk about throwing flames on the fire.

    I still contend that Wyoming is incapable of self-government and should be once again made a federal territory with NO representation in congress until it grows up.

  2. Your local conservation district has the ability to sample water quality for nutrients which may be feeding the blooms; and, in all likelihood, they are already involved. These water quality sampling programs need to extent for 5 years or more since one-time grab samples are not conclusive. Both point source and non-point source sampling can be utilized. The conservation districts qualify for grants, most likely from DEQ, to enable the work which requires certified field technicians. Oil field discharge water ( production water ), large concentrated feed lots, irrigation water return ditches, excessive nitrogen application on irrigated fields, and municipal storm water discharges are some of the potential sources of nutrients. Many of the conservation districts have mill levies which provide consistent year-to-year funding for this type of work. If you have a concern about water quality in your county, consider visiting your conservation district and attending their monthly meetings for which you can get on the agenda with a simple phone call.

  3. Great reporting Christine!
    You continue to be a top-tier, national caliber science journalist. Great job!