Home    About Us    News/Events    Projects    Photos/Maps    Join/Give    Search    Contact Us

Fish Loss in Canals

USFWS Project Leader Dave Skates with a trophy brown trout salvaged from Dinwoody Canal

Most people who have spent any time around irrigated agriculture understand that fish are killed each year when they are diverted into irrigation canals and then stranded when ditches are shut off in the fall. Although this issue has been studied extensively in the Pacific Northwest (home to endangered salmon and steelhead), very little research has dedicated to resident, inland fish loss. The Wind River watershed was fortunate to be the site of a recent study which helps fill in this gap.

Brendan McGinn, a graduate student with the Colorado Cooperative Fish and Wildlife Research Unit at Colorado State University, was the lead investigator of the research project, which studied fish loss in eight different canals on the Wind River Indian Reservation during the 2002 and 2003 irrigation seasons. The goal of McGinn’s research was both to quantify native and nonnative fish loss in irrigation canals, and to learn the timing and extent of fish movement into irrigation canals. The project used electro fishing and trap net sampling to estimate fish loss in eight canals diverting water from the Wind River, the Little Wind River, and Bull Lake Creek.

The results of McGinn’s study are truly staggering: more than half a million fish were lost during 2002 and 2003 in the eight canals involved in the study. 94% of these fish were native species and more than 20,000 were trout. Although trout were not the most common fish found in canals, they made up over half of the biomass of trapped fish. McGinn explains: “We found quite a few trophy-class fish, including Brown Trout as large as 7 pounds, Mackinaw to 25 pounds, ling to 13 pounds, rainbow and cutthroat trout up to 5 pounds, and hundreds of game fish over 14 inches.”

Fish and Wildlife Service Project Leader Dave Skates, whose office participated in the study was impressed by sheer number of fish they found in ditches sampled during the study. Skates explains, “Irrigators, sportsmen, and wildlife managers have always known that fish are lost in irrigation canals each year, but we were amazed by the number of fish we found in every canal we sampled.”

Sampling techniques on Dinwoody Canal

As impressive as the study’s fish loss numbers are, it likely represents only a fraction of the total fish loss in irrigation canals in the region. The study was only able to look at 8 of the approximately 25 major canals the Wind River watershed. If all the canals in the watershed are considered, the total fish loss in the watershed must be much, much higher.!

Although McGinn is reluctant to even hazard a guess at the actual annual fish loss in all the canals in the watershed, he agrees that it is tremendous. McGinn comments, “We found a positive correlation between canal size and number of fish, that is, larger canals trapped more fish. The largest canals in our study had a capacity of about 200 CFS (cubic feet per second). It would be really interesting to see how many fish are lost in a large canal like Wyoming Canal, which often diverts over 1500 CFS.”

McGinn explains that now is an important time to begin to understand fish loss in area canals: “First, many of the irrigation diversion structures are scheduled for replacement within the next 5 to 10 years. Second, the streams of the Wind River Indian Reservation have valuable fishery resources, both economically and intrinsically. Finally, area streams are home to several species of concern, including the burbot (ling) and Yellowstone cutthroat.”