Dam Removal on the Little Sewickley Creek

The removal of the Woodland Dam at Little Sewickley Creek is a great example of reconnecting aquatic habitats. The Little Sewickley Creek in western Pennsylvania’s Allegheny County is categorized as a “High Quality” stream by the Pennsylvania Department of Environmental Protection[1], one of the highest rankings for a stream’s water quality and ecological value in the state. Little Sewickley Creek and its watershed are popular for fishing, hiking and bird watching, providing valuable recreational and educational opportunities in an otherwise highly developed region[2].

The health of this a stream is especially notable given it sits within the highly developed environment of the Pittsburgh suburbs, where its forested watershed[3], keeps the shallow stream cool enough to support trout and other species of native fish – but wildlife can only utilize habitat they’re able to access. A direct tributary of the Ohio River, the nearly 18 miles of Little Sewickley Creek were historically connected to a vast watershed ecosystem.

Unfortunately, since 1928 the Woodland Dam (originally constructed to provide water for a nearby estate) had disconnected the majority of the creek from the Ohio River Watershed into which it had flowed. This has prevented fish from migrating up and down the stream to forage for food and to spawn. The consequences of this barrier for fish biodiversity were dramatic: while over 29 species were present just below the dam, only 7 species were present above the dam[4], despite being a cool-water, high-quality habitat. The problem was clear: the dam was a major hindrance to species mobility.

The Woodland Dam as removal work began.Photo by Little Sewickley Creek Association | Used by permission

Removing the barrier created by the dam allowed the return to the free-flowing state that the creek originally enjoyed. When heavy rains brought high water levels the following spring, the flooded creek was able to carry additional fish species upstream.

Within two months of the dam’s removal, spotfin shiners and rainbow darters, absent before, were seen a half-mile upstream of the former dam. A mile upstream, smallmouth bass were now being found in addition to shiners and darters. Fifteen months after the dam removal there were nine new species seen a mile upstream–more than doubling the fish biodiversity present before the dam’s removal. The returned species include the spotted bass, rainbow and green sided darters, longnose dace, bluntnose minnow and the bluegill[5]. This rebound is in line with what has been seen following dam removals across the United States.

Little Sewickley Creek during high water, facilitating fish dispersing upstream.Photo by Little Sewickley Creek Watershed Association | Used by permission

Revitalizing the whole ecosystem

Reconnecting Little Sewickley Creek not only gave numerous fish species renewed access to habitat, but their arrival also increased the health of the entire upstream ecosystem[6].

When streams are reconnected, recolonization by additional fish species with a variety of diets helps stabilize macroinvertebrate populations, reducing the population of some previously common insects and creating space for other species to increase and flourish[7]. In a small stream like the Little Sewickley Creek, a midsize fish like the smallmouth bass is an apex predator[8], and the return of apex fish can
have a profound impact on an aquatic environment by stabilizing populations of smaller fish and macroinvertebrates alike, enhancing biodiversity and creating a more varied and resilient ecosystem.

A smallmouth bass.Photo by Eric Engbretson, USFWS | Public Domain

References

1. Pennsylvania Department of Environmental Protection,
Little Sewickley Creek: Water Quality Standards Review & Stream Designation Evaluation Report, February 2016.

2. Little Sewickley Creek Watershed Association, About The Watershed, accessed at: https://www.lscwatershed.org 5
February 2025.

3. Civil & Environmental Consultants, Inc., Little Sewickley
Creek Watershed report assessment summary, August 2018.

4. Little Sewickley Creek Watershed Association, Woodland
Dam Removal, 27 March 2022, accessed at: https://www.lscwatershed.org/?page_id=489, 5 February 2025.

5. Ibid.

6. Eric Chapman, Director of Aquatic Science, Western Pennsylvania Conservancy, personal communication, 22 November 2024.

7. J. Ryan Bellmore, “Conceptualizing Ecological
Responses to Dam Removal: If You Remove It, What’s to
Come?” Bioscience 69(1):26–39. doi: 10.1093/biosci/biy152, 10 January 2019.

8. Marine Invasions Lab, Smithsonian Institute,
Micropterus dolomieu, accessed at: https://invasions.si.edu/nemesis/species_summary/550562, 5 February 2025.