Manmade Rock Dams: It's That Time of Year Again... Unfortunately...

A manmade rock dam deep in the New Hampshire backcountry…

While fishing in the White Mountains region of New Hampshire recently, NFC Executive Director Bob Mallard and National Chair Emily Bastian came across a small manmade rock dam. While these structures look harmless to many, they can disrupt the streambed and block fish passage, preventing them from reaching important thermal refuge and spawning habitat.

What made this dam unique was its location. We found it well off the beaten trail in the backcountry on a very lightly fished stream. While there was no evidence of fishing, there was a plastic gallon jug full of water and a small firepit built within 4-5 feet of the water, indicating that someone had possibly spent the night.

While the water was flowing over the top of the dam at the time we found it due to some recent rain, that could change quickly as the area has been experiencing hotter than normal temperatures and an overall lower than average rainfall in some areas.

It wouldn’t take much of a change in flow to turn this dam from a minor inconvenience to a potential fish passage blocking structure. And if left as we found it, it would fill with leaves in the fall which could prevent even small fish from getting upstream or downstream.

A view from upstream…

As we always do, and encourage others to do so as well, we deconstructed the dam, leaving the rocks in the streambed and both upstream and downstream of the structure. The easiest and safest way to do it is to stand on one side of the dam and pull rocks toward you. The downstream side may be your best bet as often whoever built it rolled rocks upstream to make it.

Start by creating an opening near the center of the dam to lower the water level so you can assess what needs to be done. Once things are flowing, you can roll some of the rocks to the side a bit to create channels that fish can use in low water.

After deconstruction…