WDFW undertakes innovative treatment to eliminate blue-green algae outbreaks
Update Sept. 5, 2025: During the first week of September, a small outbreak of blue-green algae was identified at the south end of Rainbow Lake. WDFW staff is working with the environmental services contractor that treated the lake initially to determine next steps.
“It’s very cloudy- pea soup-like with bright blue plaques,” said Kari Dingman, manager at the W.T. Wooten Wildlife Area in southeast Washington, about repeated outbreaks of blue-green algae at one of the wildlife area’s lakes. “We’ve invested a fair amount of money in this lake and are committed to protecting that investment to provide a safe, clear lake for the public to enjoy.”
Rainbow Lake, one of eight human-made lakes on the wildlife area in Columbia County, is managed by the Washington Department of Fish and Wildlife (WDFW). It is a small shore fishing lake fed by the Tucannon River. Rainbow Lake is well stocked with jumbo and catchable rainbow trout, making it a popular fishing spot for area residents and visitors.
“It is also an important source of water for the Tucannon Fish Hatchery, which raises endangered spring Chinook,” said Hatchery Operations Manager Ace Trump. “In the winter, 12 cubic feet per second is pulled from the lake to raise the 100,000 rainbow trout that the Department stocks in southeast Washington lakes for public recreation. That water is also used to raise up to 225,000 Tucannon spring Chinook, which are listed under the Endangered Species Act, and provides a backup water supply if needed throughout the rest of the year.”
Its’ popularity as a fishing lake and importance to the nearby hatchery make it critical to keep Rainbow Lake healthy. Blue-green algae, scientifically known as cyanobacteria, has threatened these values and interfered with activity at the lake the past two summers, making it both unattractive and potentially harmful to humans and animals. Counterintuitive to its name, blue-green algae is a bacteria that thrives in warm, nutrient-rich water. During prolonged periods of calm, sunny, hot weather (which is common in southeast Washington summers) blue-green algae can grow quickly. Blooms are becoming increasingly common on water bodies of all sizes. Blue-green algae has been confirmed in sections of the Snake River the past two summers.
These algae blooms produce toxins that can be dangerous to humans if they are ingested or come in contact with skin. Dogs have been known to die after drinking or swimming in blue green algae blooms.
In most cases, there isn’t much that can be done to treat or prevent blue-green algae. It can be prohibitively expensive and impractical depending on the size of an affected water body. In large lakes or rivers, or those with currents or moving water, wave action can shift treatment compounds, limiting the effectiveness of treatments for localized outbreaks. As a result, the usual course of action when there is a bloom is for area health districts to warn people to stay out of the water and keep pets out until the bloom dissipates.
In the case of Rainbow Lake though, being a small, managed lake, Dingman thought it could be a candidate for successful blue-green algae treatment.
“The Department has never done anything like this before,” said Dingman. “I started doing research to see if there was anything we could do to treat it ourselves. I was contacting labs all over the country to see where to send water for testing and who could help us.”
During summer 2024, Dingman spent a great deal of time researching what could be done to eliminate blue-green algae in Rainbow Lake. One thing she discovered through water testing was that the lake was very high in phosphorous, which can lead to explosive growth of aquatic plants and algae. This, in turn, can cause a variety of water-quality problems, including the growth of blue-green algae.
After many phone calls to laboratories all over the country, Dingman received a call from a laboratory technician in Illinois who recommended she look into something called Phoslock. Phoslock uses lanthanum- a soft silvery-white metal that tarnishes slowly when exposed to air- to react with the phosphorous in the water column to form the mineral Rhabdophane. Rhabdophane settles on the bottom of a water body in a state that is no longer harmful to the environment.
Once a course of action was determined- treating the lake with an algaecide first then following with Phoslock- WDFW worked with an environmental services contractor to make quick work of the treatment, using a hose to spray the compounds into the lake this past June.
So far, the treatment appears to be working.
“In past years, blooms generally started developing in late July or early August but there were definite signs of water quality degradation earlier in the summer,” said Dingman. “So far this year, there are no signs indicating a bloom is forming. The recommendation last December was to treat the lake in the spring, watch it for a year or two and add aeration if needed. The phoslock ions will continue to bind to available phosphorous in the water column until all of the ion binding sites are full. We could get 7–10 years before we will need to treat the lake again. We’ll be monitoring it closely.”
In the meantime, the work so far has improved the environmental condition and recreation value of Rainbow Lake.
