Klamath River dams create conditions suitable for toxic algae blooms, impact downstream water quality

A large bloom of toxic microcystis grows behind the Copco Reservoir dam on the Klamath River, and may impact water quality downstream. (Credit: Oregon State University).

Winding through Oregon and northern California, the Klamath River offers a vital route for migrating fish such as salmon and steelhead trout. But a host of dams, used to divert water for irrigation and to provide hydropower to nearby communities, have limited viable fish habitat and caused water quality problems for decades.

Researchers from Oregon State University have discovered that large blooms of toxic algae are forming behind the dams, and have the potential to travel over 180 miles downstream in a matter of days, causing problems in the lower reaches of the river.

Their findings were recently published in the journal Harmful Algae.

The Klamath River is important to the region, and with so many eyes on it, the algae problem there has been well-known since the early 2000s. It’s figuring out how to respond that seems to have local communities and government groups stumped.

“It’s very contentious — a lot of pressures, a lot of people jockeying to influence the river’s future,” said Theo Dreher, professor of microbiology at OSU.

“Through litigation, there’s a very intensive monitoring scheme: about a million dollars per year,” he said. “It’s pretty well looked at.”

Microcystis, a common variety of cyanobacteria, comes in both toxic and benign strains. However, previous research suggests that toxic blooms are becoming more common under a changing climate.

High levels of ambient toxins have been detected in the Klamath from time to time, raising concerns about the health of its Chinook and coho salmon fisheries, as well as the possibility of direct contact with humans or pets.

But the toxin is most dangerous when it bioaccumulates in certain organisms, such as freshwater mussels, where concentrations can be 100 times higher than ambient levels.

Certain Native American tribes are the primary consumers of these shellfish, and have used the Klamath’s waters for sustenance and ceremony for 7,000 years.

Native American tribes and environmental groups have proposed dam removal and other restoration efforts in the Klamath Basin Restoration Agreement. While many regional and tribal authorities — not to mention the U.S. Department of the Interior — have signed off on the proposal, Congress has yet to authorize it.

The OSU research was designed in part to determine if dams were somehow responsible for promoting microcystis growth, and in turn, if their removal would positively affect water quality throughout the river. Researchers focused on dams in two of the river’s major reservoirs: Iron Gate and Copco.

“We wanted to look at whether those populations of toxic microcystis that we’re seeing downstream are mostly derived from the reservoirs, or if there are areas downstream where it actually grows itself,” Dreher said.

The researchers sampled water at designated monitoring sites around the reservoirs and downstream from the dams. They paid special attention to margins close to the shore where water flows more slowly — an area underrepresented in many algae studies.

“Rather than looking at the stuff that’s just flowing madly downstream, we were looking at areas that could have supported endemic growth,” Dreher said.

Iron Gate Reservoir. (Credit: Theo Dreher).

Water samples were then filtered so that microcystis cells could be collected. Using genetic tools of their own design, the researchers compared changes in toxic algae abundance between both reservoirs and other parts of the river.

They found that changes to microcystis systems downstream — spanning at least 180 miles of the waterway — corresponded with changes occurring at the Iron Gate reservoir, leading the researchers to conclude that much of the downstream population derives from Iron Gate.

The algae even seems capable of surviving passage through hydroelectric turbines.

The OSU researchers are continuing to study the biological and environmental factors responsible for promoting dominance of either the toxic or non-toxic microcystis strains. Dreher said that the dominant strain can be supplanted by its competitor over a period of two or three weeks.

Learning more about the drivers behind these strains could enable resource managers to influence conditions that promote non-toxic algal blooms over toxic ones.

It’s likely that regular monitoring efforts in the Klamath River will need to undergo some changes before researchers can develop a greater understanding of its waters, Dreher said. Current monitoring standards rely on microscopy to identify algae cells in water samples, but toxic and non-toxic strains can be identical in appearance — plus, scientists don’t always agree on how to label these algae.

DNA sequencing provides researchers with more objective results that can be easier to compare, and is, in many cases, cheaper than microscopy. If widely adapted, Dreher says that DNA analysis could handle more samples across a greater number of sites than traditional methods.

“We think that, in the future — or even now — it’d be good for the monitoring system to change to a DNA-based system,” Dreher said.

If continued monitoring confirms that dam removal would improve water quality in the Klamath River, work would begin in 2020 to dismantle the one at Iron Gate, followed by Copco. Dreher said others could be subject for removal as well.

Dreher says it’s not his place to make policy recommendations, but the results from the study paint a pretty clear picture.

“Not finding evidence for endemic populations downriver says that the river doesn’t offer an environment for cyanobacterial growth,” he said. “If you remove the [Iron Gate and Copco] dams, the expectation would be that you have less — probably much less — exposure to the cyanobacteria.”

Of course, he noted, removing every dam in the Klamath could open new reaches of the river to algae populations.

“It’s not wise to just look at the immediate proximal area,” Dreher said.

“The bottom line is that, in a river, it’s wise to be aware of what’s upstream.”

Featured Image: A large bloom of toxic microcystis grows behind the Copco Reservoir dam on the Klamath River, and may impact water quality downstream. (Credit: Oregon State University).