POLK COUNTY -- Your best bet at finding trout within the 202,000-acre Luckiamute watershed would be in the upper west fork of the Luckiamute River.
A biological assessment shows that an 18-mile stretch that includes Beaver, Boulder and Miller creeks -- 8 percent of all stream miles in the basin -- produces about 91 percent and 45 percent of all steelhead and cutthroat trout, respectively.
Overall, however, fish numbers in the basin are low and there's a limited amount of functional stream habitat, the report also showed.
"The Luckiamute, like the Marys and Yamhill rivers and other streams that enter into the Willamette River from the west, are low elevation and heavily impacted by agriculture," said Michael Cairns, former executive director of the Luckiamute Watershed Council. Cairns helped coordinate the study.
"It gets very warm during the summer, which isn't good for native fish," Cairns said.
LWC commissioned a four-year inventory of 214 miles of streams and creeks to determine the abundance and distribution of cutthroat, steelhead and young salmon.
The work was performed by Steve Trask, a biologist and owner of Bio-Surveys, LLC, between 2008 and 2011.
Trask and his team donned snorkeling gear, waded into stream segments during the summer months and did visual counts of fish in selected pools before moving upstream, then extrapolated those numbers for the entire waterway.
Gail Oberst, a LWC board member, said the data will prove critical in identifying which parts of the basin warrant restoration projects and for seeking grant funding.
"When you do projects on sections of the creek, you have to determine how much good it's going to do," Oberst said.
The final year of the study concentrated on 85 miles of stream with the highest number of fish.
Last year, snorkelers spotted 9,745 cutthroat, most of them in the mainstem of the Luckiamute River or its upper tributaries. Only 820 steelhead were sighted and 840 coho salmon.
Cutthroat production declined each of the last three years, but didn't see large fluctuations like other species, Trask said.
Coho are a near anomaly. There were no coho salmon observed in 2008 and 2009, but a whopping 46,000 counted in 2010, most in the Luckiamute mainstem, Pedee Creek and the confluence of the Little Luckiamute and Teal Creek.
Trask explained that thousands of adult coho salmon had passed through Willamette Falls in 2009, and that a significant number ended up spawning in the Luckiamute basin the following year.
Geology affects the basin's low fish production, Trask said. The basalt and sedimentary rock formations in streams that the three native fish thrive in are limited to the west and northwest portions of the watershed. Annual rainfall is also highest in the northwest corner.
Overall, agricultural use in the basin has drained wetland and floodplains, which impacts water quality and temperatures, he said.
"The west fork of the Luckiamute, upper Pedee Creek and above the Little Luckiamute Falls are good-looking habitats," Trask said. "A lot of the rest of the basin comes out with a low habitat score."
Trask said key goals for the basin should be identifying and protecting the key "anchor" habitats and enhancing the mainstem of the Luckiamute by expanding forest buffers. Access to upstream tributaries would help juvenile fish migration during the summer, he also said.
"We assume that if you're restoring those kinds of watershed functions, you're helping lots of other species as well," he said.