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Corps Dworshak Nutrient Supplementation Study Aims To Boost Kokanee, Listed Bull Trout
Posted on Friday, January 20, 2012 (PST)

The U.S. Army Corps of Engineers Walla Walla District has offered for public comment its plan to re-implement a fertilization program in west-central Idaho’s Dworshak Dam reservoir in hope of reinvigorating the food chain and, as a result, the prized kokanee fishery and protected bull trout population.


The public is invited on the Corps’ environmental and draft “finding of no significant impact” for the “Dworshak Reservoir Nutrient Supplementation Pilot Study” no later than Thursday, Feb. 16.


This 30-day comment period is the next step in Corps’ National Environmental Policy Act compliance as it plans to resume this reservoir ecosystem stewardship pilot study that was launched in 2007 but put on hold in 2010. Unless the public comment period produces reason to pause, the nutrient enhancement program would resume this spring.


Last year, the U.S. Environmental Protection Agency issued a National Pollutant Discharge Elimination System permit to the U.S. Army Corps of Engineers effective Oct 15 after its environmental review and consideration of public comments about the project. The NPDES permit allows application of liquid fertilizer to Dworshak Reservoir as an ecosystem treatment.


The EA and draft FONSI are available for viewing at the Corps’ website at and the Orofino City Hall at 217 First St., Orofino, Idaho. Comments on the Corps’ environmental assessment must be


Any comments should be postmarked, faxed or e-mailed to the Corps by Feb. 16, to be included as part of the public record. Email comments should be sent to Faxed comments should be sent to 509-527-7832.


U.S. Mail comments should be mailed to U.S. Army Corps of Engineers, Walla Walla District, Environmental Compliance Section, ATTN: John Leier, 201 North 3rd Avenue, Walla Walla, WA 99362-1876.


The construction of Dworshak Dam in 1972 blocked fish migration on the North Fork of the Clearwater River as it converted a river habitat to a reservoir. Since construction, a nutrient-poor reservoir environment has developed. The ratio of nitrogen to phosphorus became increasingly out of balance.


The Dworshak Nutrient Supplementation Pilot Project is an ecosystem improvement program intended to improve the reservoir’s ecosystem health. The pilot project was initiated in 2007 and modeled after nutrient projects that have worked to improve ecosystem health and kokanee fisheries in several British Columbia lakes similar to Dworshak Reservoir.


Reservoir nutrient programs have been the subject of scientific studies. At Dworshak, low concentrations of nitrogen fertilizer were added to the reservoir in spring, summer and fall starting in 2007.


Adding fertilizer nutrients showed a positive impact on the aquatic species food chain, boosting the density of phytoplankton, which in turn helped zooplankton flourish. The zooplankton is the primary foodstuff for kokanee, the lake’s primary fishery. It also helps fortify small-mouth bass, another popular sport fishing target.


The program had seemed to reverse the steady decline in nutrients and improve the nutrient-poor reservoir environment.


The Idaho Department of Fish and Game partnered with the Corps’ Walla Walla District on the project designed to improve the reservoir ecosystem, which in turn enhances Idaho sport fishing opportunities.


The Corps provides fertilizer, labor and application equipment. The Corps also consults with a limnologist (a person who studies inland water systems) who “prescribes” fertilizer applications and adjustments. This consultant is a leading expert in these types of nutrient projects.


The IDFG provides the water quality and fish sampling and monitoring, sends water quality samples to the lab for testing and analysis, and monitors the kokanee fishery. IDFG also takes physical measurements such as water clarity and water temperatures at various depths.


IDFG uses kokanee salmon as an indicator species for its research because kokanee feed on zooplankton, one of the food chain organisms targeted for improvement.


Public input generated the idea for this project. The IDFG and the Corps openly communicated about the project in a series of public meetings starting before the project began operations. Appropriate actions were taken to acquire applicable permits and address requirements of other natural resources agencies.


Several agencies were consulted by the Corps prior to starting the pilot project.


-- The Idaho Department of Environmental Quality issued a consent order in 2007 that set strict water quality standards that had to be met in order to allow nutrient addition in the reservoir. The consent order was extended in 2008, and new consent orders were issued in 2009 and 2010. These standards were met during the first four years of treatment.

-- The Corps applied for a NPDES permit from the EPA on April 16, 2007, prior to the start of the pilot program. In 2010, the EPA determined that a NPDES permit was required for the project, and nutrient applications were promptly and voluntarily discontinued to allow resolution of the permit application. EPA subsequently issued a NPDES permit to the Corps effective Oct. 15, 2011, after its environmental review and consideration of public comments.

-- In early 2012, the Corps invited public comments on an environmental assessment and draft “finding of no significant impact” as part of its NEPA compliance.

-- Under initial informal consultation pursuant to Section 7 of the ESA, the U.S. Fish and Wildlife Service concurred with the Corps biological assessment that the project is not likely to adversely affect bull trout, bald eagle or gray wolves.

-- Also under Section 7 initial consultation, NOAA’s National Marine Fisheries Service concurred the project doesn’t adversely affect fish habitat.


Results during the first four years (2007-2010) of the project were encouraging. Adding nutrients initially influenced the bottom of the aquatic food chain, followed by changes at higher levels in the food chain. Monitoring results have revealed several benefits from the program including increases in beneficial algae and abundance of higher-quality food for aquatic life.


More specifically, monitoring efforts showed improvement in beneficial forms of edible phytoplankton (algae) that in turn can be eaten by zooplankton (larger microscopic organisms). As the project continued, an increase in zooplankton abundance was observed. This is important since zooplankton is the primary food source for kokanee and other aquatic organisms.


IDFG reports seeing modest increases in fish size, primarily in weight (the fish are heavier for their size). This is a good sign of ecosystem improvement. However, in a large reservoir like Dworshak, it takes several years for nutrients to work their way up the food chain. Consequently, the positive response in the fish population was just beginning to be observed in the fourth year of the program.


While not native to the reservoir, kokanee have long been the staple for anglers at the lake. They are, effectively, mitigation for salmon and steelhead that used to roam up the North Fork of the Clearwater River before that dam was built and blocked passage.


The fish have in recent years been shrinking size in large part due to a relative short supply of zooplankton. The result has been shrinking interest from anglers, according to the IDFG’s Andy Dux.


By the fourth year of nutrient additions in 2010, fish managers were starting to see results.


“There was a big increase in kokanee biomass,” Dux said. There was the same number of fish roughly as before the program started but they were bigger.


“We were starting to see a nice response,” Dux said. The program will also likely benefit bull trout, a species listed as threatened under the Endangered Species Act. Bull trout prey on kokanee.


“It’s not just impacting the kokanee,” said the Corps Paul Pence. “We’ve got a great small-mouth bass fishery.” The reservoir has twice yielded state record small-mouths, the most recent weighing in at 9.75 pounds.


With continued fertilization, more improvements are expected in the food chain and ecosystem. The kokanee are tributary spawners so their carcasses help nourish the ecosystem and its other species.


Blue-green algae blooms can be hazardous to human health, but there is no evidence that recent nutrient additions at Dworshak have caused blue-green blooms. Blue-green algae have predominated in the Dworshak Reservoir because they compete better under low-nitrogen conditions. Nutrient (nitrogen) addition is expected to promote growth of other species of beneficial algae and reduce blue-green algae.


“We truly believe that adding the nitrogen reduces the blue-green algae,” said the Corps’ Bruce Henrickson.


Over time, nutrient additions could delay the onset of blue-green blooms and lessen their severity, which would be a benefit to public health. The occurrence of blue-green algae in areas of the reservoir with no nitrogen addition is another indication that the nutrient enhancement program is not the cause of the blue-green blooms.


Public concerns have been expressed that nutrient addition in the reservoir caused disease outbreaks at the Corps’ Dworshak National Fish Hatchery (operated by USFWS), but not at the nearby Clearwater Hatchery, operated by IDFG. Scientific evaluations have not linked any hatchery disease outbreak to the addition of nitrogen to the reservoir.


A 2010 agreement allowed for additional water to be supplied directly from Dworshak Reservoir to the Dworshak National Fish Hatchery. This is the same source of water for the Clearwater Hatchery. Using water directly from Dworshak Reservoir in 2010 substantially reduced disease outbreaks at Dworshak National Fish Hatchery, providing further evidence that nutrient addition to the reservoir is not the cause of disease at the hatchery, according to the Corps.


Dworshak Reservoir water is safe for public use. The presence of blue-green algae does not necessarily mean it’s toxic. Testing is required to determine possible toxicity.


The Corps promptly responds to reports of algae blooms and has tests conducted. Drinking water is not affected by this pilot project.


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