Skip to content
Ecological Intelligence

Ecological evidence.
Independent perspective.
Explore Wild Lands ↗

Ecological Intelligence / Subject

dam removal

Peer-reviewed North America

The Elwha's insects returned in number before their river community recovered

Evidence
Peer-reviewed
Geography
Elwha River, Washington, United States
System
River / dam removal / sediment disturbance

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 ↗

Nine years of monitoring after two large dam removals show that the rebound in insect abundance and the recovery of community composition are not the same milestone.

Read the Wild Lands assessment →
Peer-reviewed North America

Chinook salmon rapidly reclaimed river miles after the Klamath dams came out

Evidence
Peer-reviewed
Geography
Upper Klamath River Basin, California and Oregon, USA; 2024–2025 surveys
System
River reconnection; salmon migration; dam removal; habitat restoration

WHAT THE EVIDENCE SAYS

After four Klamath River hydroelectric dams were removed in 2024, a multisector research team used multibeam sonar and field surveys to estimate 7,742 adult Chinook passing into reopened reaches in the 2024 migration and 13,310 in 2025. Fish reached 345 kilometers of reconnected habitat—88% of their documented historical distribution—and navigated former dam sites and modified hydraulic passages.

WHY IT MATTERS / OUR READ

The early signal is that connectivity can convert restored access into actual animal movement remarkably quickly. The next management questions are more demanding: survival, successful reproduction, cold-water refuge, water quality, species-specific run timing and whether Tribal and agency restoration goals are met over many generations.

CAVEATS / UNCERTAINTY

The 88% figure describes documented historical river length reoccupied, not recovery to 88% of the former salmon population. Counts are modeled sonar estimates for two seasons and primarily likely fall-run fish; long-term recruitment and spring-run restoration remain unresolved.

SOURCE

Goodman et al. · Scientific Reports · Klamath dam-removal Chinook monitoring
View original evidence ↗

Two migration seasons provide a quantitative measure of passage—not yet a verdict on population recovery.

Read the Wild Lands assessment →
Peer-reviewed North America

After a New Jersey dam came down, water conditions changed over years

Evidence
Peer-reviewed
Geography
Paulins Kill, New Jersey, United States; former Columbia Dam
System
River restoration; dam removal; thermal regime; aquatic communities

WHAT THE EVIDENCE SAYS

Researchers compared Paulins Kill conditions across two pre-removal years, two removal years and five years afterward at sites upstream and downstream of the former Columbia Dam. Post-removal downstream relative water temperature decreased by an estimated 0.29 degrees Celsius, while relative dissolved oxygen increased about 0.14 mg/L; aquatic indicators and fish passage also changed over time.

WHY IT MATTERS / OUR READ

The ecological case for barrier removal is not one number recorded on demolition day. Baseline and multi-year follow-up can reveal thermal, oxygen and community responses, with benefits and temporary disruptions occurring on different timetables.

CAVEATS / UNCERTAINTY

Single-river, nonrandomized before-after evidence cannot isolate every coincident driver; detected fish presence is not a measured recovery in population size. Effects depend on dam geometry and river context.

SOURCE

Frontiers in Ecology and Evolution · Columbia Dam removal monitoring study
View original evidence ↗

A multiyear river study documents a cooler, better-oxygenated relative downstream signal.

Read the Wild Lands assessment →
Peer-reviewed North America

Dam removal changed Cuyahoga fish assemblages most where reconnection opened a real route to source populations

Evidence
Peer-reviewed
Geography
Cuyahoga River, Ohio, USA
System
Urban river fish assemblages and longitudinal connectivity

WHAT THE EVIDENCE SAYS

A Restoration Ecology analysis of Cuyahoga River fish data from 1984–2024 found that removal of Brecksville Dam in 2020 increased connectivity to Lake Erie by 39 river km and more than doubled free-flowing habitat below the remaining Gorge Plant Dam. Downstream reaches gained 15 newly detected taxa and shifted strongly through time; 12 of those taxa were native and three were nonnative. Upstream assemblages showed limited change consistent mostly with redistribution of resident species rather than colonization-driven turnover.

WHY IT MATTERS / OUR READ

Barrier removal is not a binary treatment. Its ecological value depends on what the removal reconnects to, what barriers remain and whether source populations can reach the restored reach. Reconnection can support native recolonization while also opening pathways for nonnative spread, so network position and invasion risk belong in restoration prioritization rather than connectivity being treated as an automatic benefit.

CAVEATS / UNCERTAINTY

The river also experienced decades of water-quality improvement, remediation and other restoration, so not all assemblage change can be attributed solely to one dam removal. Historic sampling intensity and timing also differed from recent standardized surveys. Three of the 15 newly detected downstream taxa were nonnative, and the authors explicitly flag invasion risk—including upstream expansion of Round goby—as a tradeoff of reconnection.

SOURCE

Restoration Ecology
View original evidence ↗

Four decades of data show strong downstream turnover after the Brecksville Dam removal, while reaches still isolated by another major barrier changed far less.

Read the Wild Lands assessment →

Keep exploring

Follow the systems. Find the connections.

WildlifeLandWaterOceansClimateCitiesOne HealthGovernanceMethods / Monitoring
Browse the archive →