Every summer, visitors flock to the cool shores of Rufus Woods Lake, near Chief Joseph Dam, Washington, but within the floating algal mats that appear seasonally throughout the lake, lies a hidden danger.
Algae is a natural part of the aquatic ecosystem but some cyanobacteria, or blue-green, algae species can produce toxins harmful to people and animals.
In a two-year study, Seattle District Water Management researchers will learn more about the nature of the mat-forming algal blooms and their origins. Data gathered as part of this study will provide valuable insight into how to ensure public health and safety.
Anatoxin-a produced by some cyanobacteria in the lake is the main toxin of concern. This naturally occurring nerve toxin is harmful to mammals and can be lethal at high concentrations. Toxin levels increase as the weather warms at the start of summer, around May and June, and taper off in the fall, around September and October.
“We are doing our utmost to understand the nature of the recurring benthic bloom on Rufus Woods Lake, in the hopes of better safeguarding the public and better informing Seattle District decision makers,” said Eric Zimdars, civil engineer and co-principal investigator on the study.
Harmful algae blooms first appeared at Rufus Woods Lake around 2010. The first study in 2016 aimed at uncovering the origin of the algae and conditions in the reservoir that may have contributed to its formation. From physical sampling, researchers determined the blooms were benthic in nature and the dominant cyanobacteria genera were Phormidium and Oscillatoria. Compared to the more common planktonic algae that is generally distributed throughout the upper water column, benthic algae forms along the bottom of the lake.
Researchers started their second year of field work in May 2024and wrapped up in early September. Samples came from tiles placed in protective cages throughout the lake at different depths and physically collecting underwater cobblestones. The current study continues to work toward determining the blooms’ origin and cataloging their biological makeup.
The final report will come out in 2025.
“We collect algal covered cobbles from the boat via a dip net, and even under ideal conditions, it can be extremely difficult to retrieve those cobbles from depths of nine to 12 feet below the surface while fighting the current,” said Zimdars. “Thankfully, Chief Joseph Dam’s Natural Resource Management team has some excellent boat drivers on staff.”
For the first time at Rufus Woods Lake, researchers are using Solid Phase Adsorption Toxin Tracking (SPATT) technology to track dissolved algal toxin concentrations in the water. SPATT technology consists of a mesh-encased resin that adsorbs toxins.
“We are working together with the United States Geological Survey for assistance with sampling techniques and King County Environmental Laboratory for all toxin analysis, as well as for the building of SPATT samplers,” said Kent Easthouse, civil engineer and co-principal investigator.
The study’s data will provide valuable insight for district leaders and regional stakeholders on the issues at the lake. The Washington State Departments of Ecology (WADOE) and Health will also use the study’s cyanotoxin data to ensure public safety and inform recreators of high algal toxin levels.
Down river, U.S. Environmental Protection Agency and WADOE experts are also investigating harmful algae blooms, so USACE researchers can share information during regional meetings.
Even as this year’s harmful algae bloom season winds down, USACE experts advise recreaters to continue watching out for blooms before heading out on the water.
“In general, it’s best to avoid going into water that looks foamy, scummy, thick like paint, pea-green, blue-green or brownish red in coloration," said Zimdars. “A good rule of thumb for you and your four-legged friends: When in Doubt, Stay Out!”
To see the most recent Anatoxin-a levels at Rufus Woods Lake , head to the Washington State Toxic Algae program website: https://www.nwtoxicalgae.org/Data.aspx?SiteID=124