Dams, Fish and Mussels, oh my! Sampling the Uwharrie River, NC

A recent field trip to the Uwharrie River in North Carolina reminded me of the incredible biological diversity of Southeastern rivers. The Southeast is home to almost 2/3 of all the freshwater fish species in North America, and over 90% of the freshwater mussels. Yet much of this diversity is being lost at a frightening pace, due in part to habitat degradation by tens of thousands of outdated dams.

The Lassiter Mill Dam on the Uwharrie River is being studied for removal by the Piedmont Conservation Council, thanks to a generous grant from the Community-based River Restoration Program jointly administered by American Rivers and the National Oceanic and Atmospheric Administration. The dam has not been used in many decades since the mill shut down, and now serves only to block fish, degrade habitat, and slow the river down.

Removing the dam will help restore more natural, free-flowing conditions to the benefit of resident fish and mussels. Migratory fish, such as American shad, will also benefit– the downstream hydroelectric dams on the Pee Dee River are planning to provide fish passage, so fish coming up from the ocean to spawn will make it all the way back to the Uwharrie River for the first time in decades. Read more about American shad in the Uwharrie in an article written by the dam owner herself here.

As part of the design phase for the dam removal, a team of scientists from the US Fish and Wildlife Service, Progress Energy, NC Natural Heritage Program, NC Wildlife Resources Commission, NC Zoo, Land Trust for Central North Carolina, and American Rivers recently got together to do surveys of the fish and mussels in the river.

This data will provide a “baseline” picture of the river before the dam is removed. After the dam is removed, the team will again conduct surveys to determine how fish and mussels are benefiting.

What did we find? Upstream of the dam, in the area of slowed water, we found 40 fish of 7 different species during a brief sampling period. Sound like a lot? It did to me, until we looked downstream. Just below the dam, we found 388 fish from 23 different species during the same length of sampling.

Same story for mussels – few above the dam, many more below. What this means is that the dam is creating conditions that most fish and mussels don’t like or can’t handle- and it’s not just for a short distance, like a pond.

The upstream sampling site was a full 3.5 miles above the dam, but the river was still impounded and the fish were still impacted. The good news is that once the dam is removed and habitat is restored, we expect to see fish bounce back almost immediately, and mussels within several years.

Keep checking back for updates on this dam demolition!