Dear Candlewood Lake Community Leaders,

For more than a decade, FirstLight has voluntarily restricted our operations at the Rocky River Pumped Hydro station, largely shutting the facility down each year from the spring to the fall. This lost opportunity came at a substantial cost to our company, but we did so anyway to prevent the possible introduction of zebra mussels into Candlewood Lake through our pumping operations. We also hired Biodrawversity, a highly regarded team of experts on freshwater mussels, to monitor the lake annually for the presence of zebra mussels, reporting our findings to the Candlewood Lake Authority (CLA) and the Connecticut Department of Energy and Environmental Protection (DEEP). Biodrawversity has conducted research and provided analysis for many state, federal, and local organizations including CT DEEP.

As you are aware, the first zebra mussel was found in 2020 several miles south of our intake canal at Vaughn’s Neck. In coordination and collaboration with CLA and DEEP, we continued to maintain our selfrestriction and voluntary monitoring throughout the past two years, finding ever-increasing numbers each time we sent divers to examine the lake bottom and shoreline.

After discussing the most recent winter findings with the CLA and DEEP earlier this spring, FirstLight expanded our exploration into the deep water below the limit of seasonal drawdowns, finding zebra mussels at 25 of 31 dive sites we surveyed in June of 2022. The survey, and accompanying report, indicated that mussels were surviving at depths below the bottom limit of the drawdowns. The mussels found included many that were of reproducing age, and their size was representative of multiple years of growth and reproduction. Further, the zebra mussels are widely distributed throughout the lake from Danbury to Brookfield, up to the farthest reaches in Sherman, New Fairfield, and New Milford.

Most notably, the report concluded that zebra mussels were not only established throughout Candlewood Lake but were also capable of reproducing and likely constituted a self-sustaining population.

Since FirstLight presented these studies, the CLA announced in their most recent public newsletter that they have found zebra mussel DNA in the water column, which is additional and critical evidence of zebra mussel reproduction in the lake. This underscores Biodrawversity’s conclusion that zebra mussels are presently established, are widespread, and reproducing in the Lake.

Given this conclusion and the overwhelming evidence supporting it, FirstLight has decided to eliminate the voluntary summer pumping restriction. We do not believe the restriction, which was put in place to prevent the introduction of zebra mussels, continues to be a necessary action given the findings.

The voluntary restriction was taken out of an abundance of caution and has negatively impacted our business for ten years at our Rocky River facility, which was an impact we were willing to bear to protect Candlewood Lake from the introduction of this invasive species. Now that they are in the lake and have been identified as an established and self-sustaining population, we do not believe that such a sacrifice continues to be warranted. Rocky River is Connecticut’s largest existing energy storage facility and provides valuable grid flexibility, improves reliability of the electric grid, and helps the state avoid the dispatch of some of the dirtiest fossil fuel generators. Continuing to restrict operations at this important facility would be detrimental to FirstLight and to the ratepayers we serve.

This decision, which we do not make lightly, is based on sound scientific reasoning and is backed by overwhelming supporting evidence that zebra mussels are already present and are reproducing in Candlewood Lake. We therefore anticipate resuming regular operations when Housatonic River flows return to normal after the current drought conditions ease.


Len Greene

Head of External Affairs

FirstLight Power