What We’ve Learned from Monitoring the Patapsco River Post-Dam Removal

What do you learn watching a river for fifteen years?

Do you notice little changes along with big ones? Do the animals tell a story? Does the water share its secrets?

How does public funding investment help to restore rivers?

American Rivers has been working with a group of experts along the Patapsco River in Maryland for more than a decade to answer these very questions. It has been a monumental group effort to document the river’s response to dam removal in terms of changes to biology and physical structure.

The process of monitoring the Patapsco River started back in 2009 before the Union and Simkins dams were removed (2010 and 2011) and continued through the removal of Bloede Dam in 2018. Monitoring the river was required by regulators for five years following completion of each project to track any changes to the river and its aquatic communities.

The main goals of these dam removal projects were to:

• Reconnect historic migration routes for fish species moving between saltwater and freshwater
• Provide access to upstream spawning and rearing habitat for migratory and resident aquatic species
• Eliminate a documented public safety hazard and attractive nuisance

Monitoring the river allowed us to figure out if our projects goals were met and to ensure nothing crazy happened as a result of the dam removals.

We considered questions like— what will happen to the native fish if we remove these dams? Will migratory fish be able to access spawning habitat upstream? Will the tiny critters known as benthic macroinvertebrates (essentially, water bugs) experience any changes as a result of habitat alterations?

We also considered what would happen to sediment and water flow if these dams were removed. We contemplated questions like— how fast will the sediment leave the former impoundments and move downstream? Where will the sediment go and what will be left behind? Aquatic animals live in and on the sediment, and they may look for certain sediments for spawning, so these queries impact them as well.

I am happy to share that through the extensive monitoring effort, American Rivers and our partners have determined that the objectives of this dam removal project were achieved.

American Rivers has compiled our Patapsco River Restoration Project Research into one easy to access page: https://www.americanrivers.org/patapsco-river-restoration-project-research/. This page illustrates the depth and breadth of the vast amount of knowledge that was gained from this publicly funded effort. We plan to continue updating the site as more data and articles are published.

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Key Takeaways

Biological Monitoring

• Some species of migrating fish, including alewife and blueback herring, are making their way above the former Bloede Dam and spawning. MBSS even noted that nine species known previously to only be observed downstream of the Bloede Dam were observed upstream. (They will be making their way back up the river once again very soon, so keep an eye out for them!)
• Egg/larvae sampling results further verified that blueback herring actively spawned in the restored reach above Bloede Dam in 2024.
• Both alewife and blueback herring environmental DNA (eDNA— these are little bits of genetic material that living things leave behind in the water) was detected at sites upstream of Bloede Dam after the dam’s removal, but not before.
• American eel spread out once the Bloede Dam was removed and were climbing the eel ladder at Daniels Dam in droves.
• Benthic macroinvertebrates and resident fish seemed to recover fairly quickly after the completion of the project.

Physical Monitoring

• The physical (or geomorphic) changes to the river followed what was predicted by researchers based on site-specific modeling and monitoring results at other dam removal sites.
• The vast majority of sediment within the Bloede Dam impoundment evacuated within the first year post-removal.
• The sediment was observed moving downstream relatively quickly and causing no significant problems downstream. The river came to resemble a more natural system once again.

If you would like to dig a bit deeper into the findings of the monitoring efforts (but maybe don’t have time to read the full reports), check out this page.

What Happens Now

It’s important, especially in cases of such a significant investment of effort and public funds, to share these results with the broader community of researchers, practitioners, and regulators. Consequently, American Rivers and our partners have been presenting on this project at conferences and other events. We hope to share a series of conversations on this project with our National Dam Removal Community of Practice later this year as well.

Our partners at MBSS are working on a collection of articles for publication exploring the response of different species to the removal of the dams. Our partners at USGS are working on their second publication highlighting the sediment response to the Bloede Dam removal. A series of other publications have already been produced and can be found here. As more publications come out, we will post them to that page.

In addition, we are now talking with Maryland DNR and the broader community surrounding Patapsco Valley State Park about potentially removing the the upstream Daniels Dam. Those conversations will be ongoing this year as we work through a feasibility study and community engagement process. We offer an abundance of gratitude to our funders at the National Oceanic and Atmospheric Administration (NOAA) and the U.S. Fish and Wildlife Service (USFWS) for supporting this long-term monitoring project. Public investment in river restoration is critical to ensuring that healthy rivers are supported for the benefit of all.