North & South Rivers Watershed Association

South River Herring Can’t Get Past the Dam Fish Ladder!

In the spring, river herring migrate almost nine miles from Massachusetts Bay to the fish ladder on the South River at the Veterans Memorial Park dam in Marshfield in order to further their species, but it is there that they are being stopped despite the existence of a fish ladder at the dam. The South River in Marshfield and Duxbury is home to multiple fish species with special status and significance, including alewives and blueback herring, collectively called river herring. Herring are a vital component of the marine food chain and are prey for a wide variety of fish, birds, and marine mammals, but their populations have declined significantly from their historic numbers.

The NSRWA, with support from MassBays program and 100s of citizen science volunteers, has been monitoring river herring at Veterans Memorial Park since 2008. During that time our volunteer herring counters have observed 100-1,000+ river herring arriving at the base of the dam and fish ladder each spring. Of those, very few have been seen passing the ladder – from a high of 80 in 2012 to single digits in 2014 and 2015, 0 in 2016 and about 50 in 2017.  This year some more work at the ladder seems to be helping having seen more than 50 fish pass through the fish ladder and over the dam to date! However the numbers of fish able to successfully get over the dam through the ladder is still too low compared to what should be able to get upstream.

According to Massachusetts state law a dam owner must provide fish passage. Since Marshfield owns the Veterans Memorial Park dam, the town works with the Mass. Division of Marine Fisheries to have an Operations and Management Plan for the fish ladder that is intended to maximize function based on the ladder’s design. The fish ladder at the park requires daily observation and management to adjust to daily flow conditions. Unfortunately the ladder and the dam configurations are not well designed adding to the challenges for the fish.  A concerted team effort in 2017 and this year by of our staff and volunteers, MassDMF and the Marshfield’s DPW and Conservation staff the ladder made some headway – passing some fish but still less than 1% of those that are seen beneath the dam.

The effort needed at this site highlights the overall issue with fish ladders, namely that they require much more staffing than a free-flowing river might!

In the short term, the cooperative and active effort of all parties to adjust the boards at the dam will ensure that at least some river herring can migrate as far upstream as possible. In the long term, the town working with Veterans, NSRWA and the state is examining if this dam could be removed while retaining the aesthetics of the much beloved Veterans Memorial Park. Dam removal at this site could help preserve and improve Marshfield’s river herring population, restore this vital artery in the heart of Marshfield, diminish flooding upstream, reduce the burden of  maintenance on the town and ensure the health and welfare of our marine food chain in the future.

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