By: Stuart Winquist
Our primary focus for the Highland Pond dam removal was for restoration of freshwater habitat for diadromous (migratory) fish species. It will improve the hydrological cycle in Sawmill Brook after well over 100 years of degradation from the dam. Water temperatures will fluctuate less and remain lower in the summer, allowing the water to carry more oxygen. This benefits native freshwater fish and aquatic insect populations as well. The extended wet meadows that grew from the shallows of the former pond will filter out pollutants that wash in from the road following rain and snow melt. This benefit will be felt by the whole downstream watershed, including the Connecticut River and Long Island Sound.
After leaving our Highland Pond Preserve, Sawmill Brook passes through our Boardman Preserve less than a mile downstream, and then into the Mattabesset River in another couple of miles. A short distance upstream on the river, from where the brook enters, there is a fish passage across the StanChem Dam, which was installed in 2013. Looking at migration counts at the dam passage for Alewife and Blueback Herring, for 2014-2016 and 2021-2024, we saw the seasonal average go from about 200 to 1200 fish. We are expecting to help boost the runs in the Mattabesset by improving water quality and reducing temperature fluctuations in Sawmill Brook and the Mattabesset River. Spawning behavior is governed by both temperature and flow levels, and fish eggs and fry are susceptible to pollutants. The brook was previously passable up to the former Highland Pond dam site, so it is possible that we will get river herring spawning runs into additional habitat beyond the former dam.
One question we did get during the planning of this project was, “What will happen to the wildlife that used the pond?” It is a fair question to ask. The pond was heavily degraded by nutrient loading, as can be seen in the pond aquatic growth in the photo. However, in the spring and fall, it did host its fair share of migrating ducks.
The stream had been pumped around the dam site starting July 1 at the start of the project, and my visit on November 8 was the first time I had been back after the stream flow had been returned to its original channel. I am happy to report that on that visit, I found quite a number of ducks in the remaining ponded shallows in the meadow. My eBird count for ducks was five Wood Ducks, eight Mallards, seven American Black Ducks, and 20 Green-winged Teal. The Teal were interesting because they were constantly moving as an exploding flock, from the open water, back into hiding in the marsh grasses, presumably to feed, and then back to the water. Teal are known to spend more time than other ducks foraging on flats adjacent to the water.
November 8 was one of those last warm days of fall, and in the grass at the edge of the former pond, I found two Northern water snakes basking in the last warm glow of 2025. When I returned on Dec 10, all of the ponded water was frozen, the snakes were hidden in hibernation, but five Mallards still foraged in the flowing water in the stream.
Certainly, the environment will change as it recovers and becomes a bridge between dry land and water. Beavers that have inhabited the pond in the past will no doubt engineer some of those changes. We are looking forward to watching the changes and enjoying the wildlife we find in the streams and wetlands that have replaced the man-made pond—and in the brook below as it changes too. Hopefully, our rewilding of a little corner of our neighborhood will contribute to the recovery of Long Island Sound, and the growing number of seals, dolphins, and whales in Connecticut’s backyard.