WHAT THE EVIDENCE SAYS
Following removal of the Elwha and Glines Canyon dams, more than 20 million tonnes of reservoir sediment moved downstream as passage reopened to more than 90% of the watershed. Across five river reaches and nine years of observations, benthic invertebrate density fell as much as 95% during active removal, then returned near baseline within roughly three years of peak sediment transport. Taxa richness and community composition, notably some caddisflies and longer-lived groups, remained altered after that interval.
WHY IT MATTERS / OUR READ
The ecological signature of a restoration project can contain immediate disturbance, recovery in one metric and prolonged change in another. Restoration success criteria should distinguish connectivity, organism numbers, sensitive taxa and community composition; the years after construction are part of the intervention, not an optional follow-up.
CAVEATS / UNCERTAINTY
Observational before-during-after monitoring was conducted in one very large dam-removal system, with fish recolonization, sediment and habitat succession interacting. A numerical rebound does not prove all functions or populations are restored; these outcomes do not imply dams should remain.
SOURCE
Frontiers in Ecology and Evolution — Morley et al. (2026)
View original evidence ↗