BOISE, Idaho (AP) — A multiyear study of mercury contamination is underway in a three-dam hydroelectric project on the Idaho-Oregon border that's part of a power company's effort to renew its license with the federal government.
Idaho Power says the five- to eight-year study now in its second year is needed to better understand the high mercury levels in fish in the Hells Canyon Complex on the Snake River.
The mercury working its way up the food chain appears to be the result of a chain reaction that starts with nutrients from upstream agricultural areas, according to scientists with the U.S. Geological Survey who are running the study.
Researchers say 96 percent of smallmouth bass in the system contain so much mercury they're unsafe to eat under Oregon standards. Under Idaho's less stringent standards, that drops to 31 percent.
"The mercury concentrations of fish within the complex are up to five times higher than within fish upstream of the complex," said Austin Baldwin, a hydrologist with the U.S. Geological Survey based in Boise.
The elevated mercury levels in fish also extend at least 60 miles downstream to the Salmon River confluence.
The high mercury levels are preventing the utility from obtaining approval from Oregon and Idaho, and that's preventing the Federal Energy Regulatory Commission from issuing the company a new, multi-decade license. The previous 50-year license expired in 2005, and the company has since been operating the complex on annually issued licenses.
The company supplies electricity to customers in southern Idaho and eastern Oregon, and the Hells Canyon Complex is one of its key power producers.
The main takeaway from the study so far, said Ralph Myers of Idaho Power, is the realization of the complexity of the problem.
"It really is more of a watershed-scale issue than something where you can just focus on the reservoirs," he said.
Results from the study so far have discovered a process where nutrients enter the uppermost reservoir formed by Brownlee Dam, which is also the largest of the three reservoirs.
Scientists say the nutrients, combined with warm summer temperatures, lead to an increase in algae and organic material. That's broken down by oxygen-using bacteria leading to depleted oxygen levels in the reservoir.
The reservoir becomes stratified by late summer, with deeper areas becoming devoid of oxygen. In those areas, bacteria that don't use oxygen, called anaerobic bacteria, go to work on inorganic mercury that enters the system mainly through the atmosphere.
Baldwin said the process isn't fully understood, but anaerobic bacteria transform the inorganic mercury to methylmercury, with the amount increasing in the reservoir through the summer and fall.
Methylmercury is much more harmful than inorganic mercury, scientists say. It also accumulates in organisms and works its way up the food chain to fish.
"If you eat a fish, then you get all that mercury from that fish," Baldwin said.
The study has found the process occurring in all three reservoirs.
Idaho Power doesn't have control over what comes into the system from upstream, Myers said, but the company is looking at finding ways to reduce the amount of nutrients entering the Snake River from the agricultural areas.
"What we would be doing would be going out and working with landowners, and looking at riparian conditions on the tributaries," he said. "Look for ways that we can promote cleaning things up upstream and improving conditions in the reservoir."
He said the company is helping fund irrigation upgrades in some areas that could reduce agricultural runoff into the Snake River.
Another problem the company faces in getting relicensed is water temperature and oxygen conditions in the reservoirs, which scientists say are likely tied into the same conditions causing the mercury problem.
Water temperature is a concern because cold water from the reservoirs could be used to help federally protected bull trout and fall chinook downstream with cold-water releases from the dams.
However, Baldwin said, cold water from deeper in the reservoirs could also put more methylmercury into the Snake River.
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