Column: Manmade dams and rock piles can cause major negative ripple effects in our waterways

This photo of a dead hellbender near a manmade rock structure was widely circulated when people became more aware of the potential negative impacts of cairns (manmade rock piles created as landmarks or monuments). The construction of the tower in the background may have led to this hellbender being crushed, according to one source. Image by David Herasimtschuk.

Riverkeeper's note: The following column was written by Middle Susquehanna Riverkeeper Association Northern Tier Regional Director Emily Shosh. 

While man-made rock dams might seem like a fun spot to swim and recreate, these structures may unfortunately have negative effects on the stream, aquatic organisms, people and pets.

​Rock dams, cairns (a heap of stones set up as a landmark, monument, tombstone, etc.) and other manipulation of stream substrate are not recommended, especially in headwater streams.

Some of their threats include:

• Loss of habitat and shelter for hellbenders, fish, amphibians and benthic macroinvertebrates.  
• Barriers to native fish and other aquatic organisms - perhaps the biggest issue of them all, leading to genetic isolation and less resiliency in species over time. Also, in the summer when fish need to move into the colder headwaters, impassable rock dams may trap fish in lethally warm areas.  
• Destruction of the stream substrate’s microhabitats of benthic macroinvertebrates, which affects the aquatic food chain.
• Accelerated erosion - depending on how the dam is situated, water may re-route in a direction that could lead to undercut banks, unnatural erosion and sedimentation.

Rock dams, cairns and other manipulation of stream substrate are not recommended, especially in headwater streams where native brook trout and hellbenders thrive. We strongly advise against this destruction of natural resources.

If cairns in a stream are found, they should be toppled over. Generally, this does not require a permit. However, do not trespass onto private property to dismantle these structures.

Eastern hellbenders in particular require large, flat rocks for shelter and breeding. This means that the manipulation of those rocks for cairn or statue-building is especially detrimental to our already threatened state amphibian.

​Read more on the Riverkeeper’s Hellbender work here.

If you find a rock dam on public land, it is a good idea to first contact the State Forest, Game Commission, Fish and Boat Commission or state parks depending on the site location.

One example of such a project was undertaken in 2022 by the PA Chapter of Native Fish Coalition on Bushkill Creek in Delaware State Forest.

​The group worked directly with DCNR to procure the proper permitting.

A full write up on the project and additional pictures can be found here. ​

A small stream in the White Mountain range of New Hampshire is restored to its natural flow. Images courtesy of Bob Mallard, Native Fish Coalition.

A side view of the affected Bushkill Creek in Delaware State Forest. Image courtesy of PA Native Fish Coalition.

A before photo of a project to dismantle a rock dam was undertaken by the PA Chapter of Native Fish Coalition, in collaboration with the Delaware State Forest. Below is the after photo. Both images courtesy of the Native Fish Coalition.

Additional resources:

• Chione, A. (2018, August 18). Knock ’em down: Recreational rock dams pose a challenge to native fish. Native Fish Society. https://nativefishsociety.org/news-media/knock-em-down-recreational-rock-dams-pose-a-challenge-to-native-fish 
• Diaz, L. (2019, October 6). The desperate plea of the Hellbender: A symbol of ancient Appalachia. Beyond the Riverbend. https://beyondtheriverbend.com/2019/10/06/the-desperate-plea-of-the-hellbender-a-symbol-of-ancient-appalachia/ 
• Holappa, K. (2019, July 3). Fish biologists ask recreators not to build rock dams in local rivers. Daily Record. https://www.dailyrecordnews.com/news/fish-biologists-ask-recreators-not-to-build-rock-dams-in-local-rivers/article_7e5c0220-6bee-524a-a938-c184e02e5fdf.html 
• Zazworsky, D. (2021, June 3). #KickRocks campaign stands up against Cairns. Flylords Mag. https://flylordsmag.com/kick-rocks-cairns-campaign/ ​