by Zachary Lehmann
Removal of the second of three Raritan River dams in Somerset County, New Jersey began on July 23, 2012. The dam removal is a result of an agreement between the New Jersey Department of Environmental Protection and Coastal Eagle Point Company. As the biggest of the three dams, the Roberts Street Dam removal represents a great step forward for restoring anadromous fish populations and their natural habitats.
Fish populations worldwide are struggling to survive the effects of declining water quality, reduced habitat ranges, increased fishing pressure, and changing trends in weather patterns. In the United States alone, striped bass populations are a fraction of what they were a decade ago, salmon runs have decreased significantly on both coasts, and invasive species are overrunning native local species.
Dams present one of the largest obstacles to natural fish migration. Fish ladders, constructed to allow fish to migrate upstream to reach essential spawning habitats, only create additional obstacles. Not only are fish forced to swim through strong currents that would otherwise not exist, the ladders also create a bottleneck allowing only a few fish to swim through the narrow passage at a time. As a result, fish begin stockpiling in front of the dam which makes them easy prey for predators.
Making it through the dam gauntlet is only the first challenge. Upstream dams create pools of warm, slow-moving water, which causes sediment suspended in the water column to settle in the riverbed. As the sediment settles, it buries fish spawning and foraging habitats that are essential to their life cycle. Warmer water also reduces the dissolved oxygen levels, threatening their ability to survive.
Prior to the dam removals, Great Ecology conducted a Cost Benefit Analysis and is eager to monitor the effects and verify our predictions. Fish populations are expected to flourish as the dam removal will reconnect over 35 river and tributary miles, increasing the fish spawning area almost ten-fold, significantly benefiting the ecology and local economy of the river and its tributaries.
Unless we continue to take bold actions such as dam removal, fish populations will progressively decline. While fish ladders are better than no bypass system at all, they are not enough.