Irrigation Canals and Fish.
FOR DECADES WE'VE KNOWN THAT irrigation canals can rob trout streams of water; we're just now beginning to understand the degree to which irrigation canals can rob trout, salmon, and steelhead streams of fish.In many parts of western North America, water for irrigation is taken from the nearest available source. Though lakes and reservoirs are used, streams and rivers are often preferred because they flow through a great spectrum of land, stretching like veins from mountain sources through the arid farmland of the foothills and Western prairie. At numerous locations along its journey, water is diverted out of streambeds into canals where it becomes available to irrigators. Unfortunately, many of the streams used for irrigation are home to resident trout, or routes to spawning areas for anadromous fish such as steelhead and Pacific salmon.
The familiar problem posed to sport-fish streams by the irrigation industry is simple: Fish and agriculture both need water. Unfortunately, agriculture needs water most during hot, dry summers when streams have the least water to give. If too much water is removed from the stream, what remains gets too warm, resulting in dissolved oxygen deficiencies and possible fish-kills. Many of western North America's best known streams have faced this problem, including the Big Hole, Beaverhead, and Gallatin rivers in Montana; the Big Wood River and Silver Creek in Idaho; and the Oldman and Bow rivers in Alberta.
Recent efforts in southern Alberta have confirmed another problem related to irrigation, one whose seriousness has not been as widely documented or understood. Resident fish in rivers and anadromous fish migrating to and from spawning areas often move into irrigation canals, simply because there is nothing to prevent them from doing so.
Fish can often be quite healthy and presumably happy in an irrigation canal--for a while. The problem begins when the supply of water to the canal is turned off in autumn after the irrigation season has ended. The fish in the canal simply die as the water disappears. The river system is robbed of some of its population because fish move into the canals and don't return to the river.
Biologists suspected the problem in the Western U.S. early in the 20th century, and in the 1940s the state of California began screening some of its irrigation diversions to keep fish from entering them. In 1958 and '59, a study on the Salmon River drainage in Idaho concluded that a screening program there would save as many as one million Chinook salmon smolts.
There has been little documentation of losses of resident trout to irrigation canals, but one of the first occasions was a report in 1910-11 to the Dominion, Alberta, and Saskatchewan Fisheries Commission: "The subject of irrigation ditches came prominently before the commission, especially in southern Alberta, and there was abundant evidence to show that considerable damage had been done and is being done to the fisheries of these streams, by the lack of proper screens."
The problem in Alberta was uncovered in a tangible way in 1983, when the provincial government introduced an herbicide into the Carseland Irrigation Canal--a diversion of Bow River water near the town of Carseland--to kill accumulating aquatic plants. The procedure also killed 11,000 fish that were living in the canal at the time, 1,200 of which were trout and mountain whitefish. The dead fish were gathered through the placement of block fences across the canal. Several of these fences washed out under the weight of dead fish trapped against them.
In 1986, while doing research for my book Blue Ribbon Bow, I was advised that fish loss to the Carseland Canal was a problem of undetermined severity, but was expected to be addressed in the near future. In 1993, after seven years of waiting, Trout Unlimited (TU) Canada proposed evaluating the loss of fish in the Carseland Canal jointly with the provincial government. The proposal was rejected.
Then in 1996 TU Canada independently conducted its first "Fish Rescue." On an October day, 40 TU Canada volunteers used a block net at a single site on the canal, and caught and returned 2,830 trout and whitefish to the river. The program was expanded in the fall of 1997, when 60 volunteers worked at two sites on the canal for four days and captured 16,350 sportfish that would have died when the water was turned off.
In 1998, Fish Rescue became a huge operation: 320 volunteers spent 14 days on the upper five miles of the Carseland Canal. The number of fish returned to the Bow River from the irrigation canal during the two weeks was stunning-- approximately 90,000 sportfish and 35,000 nonsportfish.
The effort struck a chord with the local community and was publicized by local and national media. The event was covered by major newspapers throughout Alberta and also by the Canadian Broadcasting Company (CBC) National News. On one day, the story was reported by six television stations. At an impromptu press conference at the rescue site, TU Canada Bow River Chapter President Alan Harvie said that the organization hoped it was now obvious that the real solution to the problem is not an annual fish rescue, but rather a fish-exclusion device that prevents fish from entering the canal in the first place. TU Canada is pressing the Alberta government to establish a task force to study the problem and develop corrective actions. As of October 1999, the government hasn't responded.
There are disturbing visions. The Alberta rescue occurred on just five miles of one canal on one trout stream. Studies have been conducted by TU on six other canals that divert water from Alberta streams (including the Oldman River), and in each case significant fish loss has been documented. Thus, TU Canada estimates that the number of sportfish lost to irrigation canals in Alberta reaches into the millions.
What about the rest of western North America? In Idaho there is no documentation of the severity of the problem on trout streams, but Douglas Megargle of the Idaho Department of Fish and Game says that fish loss is significant in some places, particularly in low-water years when more water is diverted into the canals than is left in the streambeds.
Megargle and other scientists believe that the problem is most severe for anadromous fish and for trout that migrate great distances to spawn. During migration, a greater number of fish pass diversion points where they can leave the river and move into a canal. There is less difficulty on streams like the Big Wood River, where trout move short distances to spawn, than there is on other streams, where they move greater distances.
There are no plans for installation of more exclusion devices on Idaho's trout streams, even though over 200 rotating-drum screen-type exclusion devices have been in place since the 1970s on the Salmon River and its tributaries to prevent the loss of migrating salmon smolts. Idaho's trout streams don't have the benefit of the federal funding that is provided to anadromous fisheries management. Idaho estimates the cost of installing rotating-drum-type exclusion devices at about $1,000 for each cubic foot per second (cfs) of water flowing in the canal. The will to address the problem exists, but so far the dollars do not.
Eric Reiland, biologist for Montana Fish, Wildlife and Parks, prepared a thesis on fish loss to irrigation canals for his master's degree at Montana State University in 1997. His study area was the West Gallatin River near Bozeman. He observed that certain canals captured a great number of fish, while others, for unknown reasons, did not. Reiland is reluctant to generalize about the severity of the problem because it seems to vary widely in different locations.
There are fish exclusion devices operating today on a number of Montana trout streams, including the Yellowstone, Gallatin, Blackfoot, and Big Hole rivers. Montana's plan is to continue to investigate the problem and add screens to the diversions that require them. Special attention is being given to the diversions on streams where species of special concern are found. Currently the most work is being done on the Blackfoot River and its tributaries, where a benefactor will be the threatened native bull trout.
In Oregon, two U.S. House representatives have recently proposed legislation that would help pay for the costs of fish-exclusion devices in Oregon, Washington, Montana, and Idaho. The bill is supported by numerous conservation organizations, sport- and commercial fishing groups, and the Oregon Water Resources Congress. No further action had been taken as of October 1999.
Clearly the loss of fish to irrigation canals is not a simple problem to quantify. Some diversions operate without significant fish loss, while others Severely impact fish populations. Reducing or eliminating fish loss to canals will require retrofitting existing irrigation diversions with fish exclusion devices. That will boil down to the eternal need for dollars.
TU Canada estimates that the cost of solving the problem in southern Alberta could be $16 million--a significant amount of money, but perhaps not unreasonable when compared to the $12 million the province is currently prepared to spend to upgrade a single siphon on the Carseland Canal.
Biologists, conservationists, and legislators are in the early stages of an evolution of understanding of the canal/fisheries problem. It is clear that fish loss to irrigation canals is a problem in certain places. And in case our steelhead, trout, and salmon don't face enough difficulties today from logging, mining, development, netting, acid rain, and overfishing, we've now identified one more problem that fisheries conservationists must solve.
JIM McCLENNAN owns Country Pleasures Fly Shop in Calgary, Alberta. He is the author of Blue Ribbon Bow (Johnson Gorman Publishers, 1986 and 1998) and Trout Streams of Alberta (Johnson Gorman Publishers, 1996).
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| Author: | McLENNAN, JIM |
|---|---|
| Publication: | Fly Fisherman |
| Geographic Code: | 1CALB |
| Date: | Feb 1, 2000 |
| Words: | 1630 |
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