NYC to Study Possible Expansion of Cannonsville Reservoir as Part of Drought Planning

A new study could revive a decades-old proposal to enlarge Cannonsville Reservoir, a key part of New York City’s water supply system in Delaware County.

New York City Department of Environmental Protection officials told the Upper Delaware Council on Aug. 6 that the city is preparing to study whether Cannonsville Reservoir could be expanded to increase water storage and help mitigate future droughts.

The study is one of four options advanced from a 2023 Delaware River Basin Commission study that examined 2,500 potential ways to increase water storage in the basin. The other options include three quarries.

The Cannonsville study is pending an intergovernmental agreement between the DEP and DRBC. It could begin in late 2026 or early 2027.

Officials say the study will examine facilities, land ownership, operations, geology and structural issues, environmental restrictions, permitting and costs. It also will consider the potential effects on wetlands and upstream areas, impacts to roads and bridges, financial effects on ratepayers and the cost-benefit of the project.

The proposal has a long history.

A 1982 Good Faith Agreement included a recommendation that New York enlarge Cannonsville Reservoir if feasibility and environmental studies determined the project was practical. A state study completed in 1986 found the expansion technically feasible, but cited significant financial and environmental challenges.

The earlier proposal would have required the purchase of 118 acres and was considered financially feasible only if hydropower were added. The plan was not pursued.

The new study comes as New York City continues planning for major repairs to the Delaware Aqueduct, which carries about half of the city’s drinking water.

The 85-mile aqueduct runs from the Rondout Reservoir in the Catskills to the Hillview Reservoir in Yonkers. It was placed in service in 1944 and is described by DEP as a critical component of the city’s water system.

A major bypass tunnel project was designed to address leaks in the aqueduct. The leaks, discovered in 1990, are estimated to account for about 20 million gallons of lost water each day under typical conditions. About 95% of the leakage is from the Newburgh section.

The city shut down the Delaware Aqueduct in 2024 to make connections to the new bypass tunnel. But the shutdown was halted after sudden drought conditions developed. The project now requires a new procurement process.

The drought highlighted the need for additional planning. NYC DEP said the fall of 2024 brought an 8-inch rainfall deficit to the watershed, while October and November ranked among the driest such months on record. From June 2024 through June 2026, 18 of 24 months had significantly less precipitation than historical averages.

DEP expects a new contract for the Delaware Aqueduct bypass work to go out for bid around 2029. A shutdown to complete the connections is planned for 2031-32 and is expected to last six to nine months.

Image: Located at the western edge of Delaware County, southwest of the Village of Walton and about 120 miles northwest of New York City, Cannonsville Reservoir is formed by damming the West Branch of the Delaware River, which continues south and becomes part of the lower Delaware River, the border between New York and Pennsylvania. It was placed into service in 1964 and holds 95.7 billion gallons at full capacity. (NYC Water)