The Challenges and Costs of Urban Dam Removal Compared with the Response of Diadromous Fish on the Mill River, Massachusetts

Thousands of mill dams dot the New England landscape.  Many are located on urbanized, degraded river segments, blocking access for diadromous fish to higher quality habitats upstream.  Urban dam removal projects are expensive; thus, monitoring is essential to determine whether the cost of an urban dam removal is worth the benefit.  The goal of the Mill River Restoration Project is to remove three dams and build a fish ladder at a fourth while monitoring the response of diadromous fish.  The dams are in an urbanized setting, but their removal will provide access to more than 30 miles of higher quality habitat.  A partnership of federal, state, and local organizations removed two dams and built the fish ladder in 2012 and 2013.  The final dam will be removed in 2016.  To date, the partners have monitored the response of diadromous fish to newly available but degraded habitat.  Once the last dam is removed, we will monitor the response of diadromous fish to availability of higher quality habitat. This presentation discusses the challenges and costs common to urban dam removal compared with the results from the first two years of data collection, focusing on alewife, sea lamprey, and American eel.