"The statement that a hydro-electric plant can pump its own water supply sounds absurd on the face of it, yet this is virtually what happens in the case of the Rocky River Hydro Plant..."
- Chief Engineer Paul Heslop, Connecticut Society of Civil Engineering meeting, 1928
Most residents of western Connecticut know 11-mile long Candlewood Lake as a recreational resource for boating, fishing, and swimming. Not many are aware that the lake is part of the first major project in the United States designed to generate electricity from water pumped into a reservoir. The project's design is made possible by the economics of the electricity market, where power provided during periods of greatest demand generates the highest rates.
To create Candlewood Lake, builders dammed a pair of tributaries to the Housatonic River, forming the basis for the reservoir. The eight-square-mile storage area is then filled by pumping water from the Housatonic at periods when electricity to run the pumps is least expensive. Power generated by releasing the same water can then be sold at higher rates during periods of peak demand. The technology pioneered at the Rocky River project-reversible pumps that also act as generators-was not widely used in other U.S. projects until the 1950s and 1960s.