Fish mortality associated with irrigation ditches is a problem throughout the West. In Montana alone it is probable that hundreds of thousands, if not millions of fish (not all are trout) perish in irrigation ditches on an annual basis.
Trout Unlimited is working to raise funding for, and install screening on irrigation ditch headgates, but progress is slow. Additionally, many regional TU chapters are hosting events in cooperation with landowners to rescue fish stranded in irrigation ditches.
A fishing buddy and I recently held our own unsanctioned fish rescue on the irrigation ditch that runs by my house. This ditch diverts water from the Gallatin River, and likely claims the lives of thousands of fish every year. In about two hours of work with a boat net, a bucket and a sheet of window screening we managed to rescue nearly 100 fish. Many of them were fingerling whitefish, but a number of them were fine brown trout that belong in the river.
Our efforts were just a drop in the bucket, but every bit helps. Contact your local TU chapter to learn more about opportunities to get involved.