Keep ’em in the river! Reconsider irrigation water diversion policies to avoid salmon deaths

Across western North America, juvenile salmon and other migratory fish are killed in irrigation systems, which has population-level impacts for species at risk. How to reduce or prevent these deaths is an important policy issue. Federal policy in the United States requires that fish be screened from water withdrawn from rivers containing salmon and prescribes screen designs in irrigation canals to return fish to the river. A recently published study demonstrated that juvenile salmon survival was 10–37% lower for fish that entered a diversion channel and were screened and returned to the river compared to fish that remained in the river and were passed over a diversion dam. An independent study demonstrated that hydraulic patterns at in-river screening structures can allow most fish to bypass the water withdrawal and remain in the river, whereas screens in irrigation canals stressfully concentrate the fish before sending them back to the river, where they are especially vulnerable to predation. Present policies favoring in-canal screening warrant re-examination to include in-river screening methods that can increase fish survival by keeping them in the river.