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HERMISTON, Ore. -- Oregon State University researchers in collaboration with scientists from the Confederated Tribes of the Umatilla Indian Reservation are researching what happens to fish and invertebrates when water from the Umatilla and Walla Walla rivers is diverted for irrigation purposes in neighboring basins.

Many western rivers are used for irrigation during the summer months, and agriculture often competes with fish for water use. This competition has been hotly debated across the west since 2001 when irrigation to most of Oregon's Klamath Basin was cut off to protect threatened coho salmon.

"There's a lot of interest in trying to leave more water in the river for fish," said David Wooster, a riparian entomologist at OSU's Hermiston Agricultural Research and Extension Center, and the project's lead investigator. "But there is actually very little science about water levels in rivers and at what point you see an impact of water withdrawal on fish and invertebrates."

In the course of the OSU project, which is funded by a $465,000 grant from the USDA National Research Initiative Competitive Grant program, Wooster said he hopes the team of researchers can aid water managers in assessing irrigation strategies by providing them with useful, accurate information about the impact of diversions on river dependent organisms.

He said that "in no way" is the project meant to be a critique of surface water use for irrigation.

"We're in an area with a limited supply of water, and a high level of agriculture that's incredibly important to the economy," Wooster said, adding that stakeholders in the basins have a history of working together toward watershed health. "So far, the different parties involved in the water issue have done a very good job of cooperating. This work has the opportunity to assist in the understanding of water withdrawals and help guide policies about irrigation that may otherwise by detrimental to irrigators."

Researchers have already conducted numerous research projects looking at changes in water quality, temperature and flow on the rivers, but the OSU project is unique in that it is looking at what happens to the rivers' biota, said Jesse Schwartz, the research, monitoring and evaluating program director for the tribes' Department of Fisheries.

To do this, the scientists will determine whether the effect of water withdrawal is consistent with a proportional model, where the response of the ecosystem is proportional to the amount of water withdrawn, or a threshold response model, where there is little response below the threshold, but a large response above the threshold.

"Responses can take two forms," said Schwartz. "One response to diversion could be a change in the abundance of what's there. We could simply see fewer critters. Or we could see a change in what's living and moving around there. Right now, we don't know what to expect, and it's possible that we won't see either response."

The team of researchers will not only examine the responses of fish and invertebrates in the river, but also organisms in the riparian area adjacent to the river, said Sandy DeBano, a riparian entomologist in OSU's College of Agricultural Sciences.

USDA National Research Initiative grants support important, high-priority research in the biological, environmental, physical and social sciences that is relevant to agriculture, food and the environment.