Irrigation canals threaten the Bow River’s world-class sportfishery. Here’s what you need to know


Ongoing concern extends throughout Alberta’s angling community regarding a decline in populations of mature trout in the Bow River, both in Calgary and downstream of the city. Provincial biologists have identified several major stressors on the fish, from erratic and declining flow levels to catch-and-release angling mortality. As it stands, it appears the province only intends to tackle the problem through potentially severe restrictions on fishing seasons and/or angling methods. That was first discussed in this space earlier this year (see

However, biologists have also identified another major factor contributing to fish mortality: irrigation canals. “Big fish loss is almost always a harvest or entrainment issue,” says Michael Sullivan, a fisheries biologist with Alberta Environment and Parks. The critical word here is “entrainment,” the term for the loss of fish when waterways are diverted for irrigation or other reasons.


In the case of the Bow River, trout are able to enter two irrigation canals during the summer, one in Calgary and one near the town of Carseland. When the water supply to the canals is shut off in the fall following  the irrigation season, many of those fish become trapped and die as the canals dry up. Addressing this significant threat to the Bow’s trout should be a top priority.


How many fish are lost each year? No one knows for sure, although Trout Unlimited Canada has been conducting its annual Fish Rescue every October since 1998, capturing and returning fish to the Bow. In 2022, for example, more than 4,000 sportfish were rescued from a very small portion of the Carseland canal alone, along with an almost equal number of critical forage fish. To date, more than a million fish have been returned to the Bow and other rivers with diverted waters, such as the Oldman.


But here’s the thing: we’ve known about this problem for a while. “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 (exclusion) screens.” This comes from a report to the Dominion, Alberta and Saskatchewan Fisheries Commission in the year—wait for it—1910.

Fish rescues remain a must (photo: Trout Unlimited)

Fast-forward to 1998. After the first fish rescues that year, TUC president Alan Harvie said he hoped it was obvious the real solution to the problem was to prevent fish from entering the canal in the first place—not annual rescues after the fact. A quarter of a century later, still nothing has been done to address entrainment.



People may wonder why this problem is such a concern now, since the Bow has managed to cope with it this long. The answer is that other stressors are increasing every year, including rising water temperatures, an apparent worldwide decline of trout-stream insects, and the negative pressures placed on the river by the city of Calgary. The Bow can no longer simply absorb fish loss due to entrainment.

Fish rescues help, but they treat the symptom, not the cause of the problem. Instead, the solution likely requires the installation of physical structures to prevent fish from entering the canals in the first place. That’s dependent on the will of the provincial government, however, and the eternal need for dollars.

How many dollars? Answering that will require more research, perhaps starting with a look at how other jurisdictions beyond Alberta’s borders are dealing with the issue (there are numerous rivers in the U.S. northwest, for example). As for who will foot the bill, that’s another question.

The Alberta government—via Alberta Environment and Parks—owns the diversions and canal headworks, while the Bow River Irrigation District and the Western Irrigation District own the canals proper. Irrigated agriculture contributes approximately $6.5 billion to Alberta’s GDP, so it’s not much of a stretch to think the irrigation industry should provide a significant portion of those dollars.

A new organization called The Trout Trust has been formed in Alberta to raise awareness of this issue, and to persuade the provincial government and the irrigation districts that the time has come to fix the problem. A century is far too long, don’t you think?

Western view is an opinion column. We invite constructive discussion of the various issues raised here.

For more on the Trout Trust, visit