One of the most prominent landscape and cultural features of the Catskill and Hudson Valley regions is the 2,000 square mile New York City Watershed. The watershed is the largest unfiltered water supply in the U.S., providing 1.4 billion gallons of clean drinking water each day to over nine million residents in New York City and some smaller municipalities (nearly half the population of New York State). Approximately 10% of New York City’s water comes from 12 reservoirs and three controlled lakes east of the Hudson River in Westchester, Putnam, and Dutchess Counties. This ‘East-of-Hudson’ portion of the watershed comprises about one quarter of the 2,000 square mile watershed area. The larger watershed area lies West-Of-Hudson, in Delaware, Greene, Schoharie, Sullivan, and Ulster Counties.

Six large reservoirs in the Catskill/Delaware Watershed hold a total capacity of about 550 billion gallons; 90% of the NYC water supply. The two reservoirs in the ‘Catskill’ portion of the watershed are the Ashokan and Schoharie Reservoirs, and they are fed by the Esopus Creek and Schoharie Creek respectively. Water from the Schoharie Reservoir is carried to the Esopus Creek and Ashokan Reservoir via the Shandaken Tunnel. The ‘Delaware System’ is comprised of the Cannonsville Reservoir, fed by the West Branch Delaware River, the Pepacton Reservoir, fed by the East Branch Delaware River, the Neversink Reservoir, fed by the Neversink River, and the Rondout Reservoir, fed by Rondout Creek; these too are connected to each other and to NYC by underground tunnels.

The construction of the West-of-Hudson reservoirs, tunnels, and other infrastructure was initiated in 1905 and conducted through the 1960's. Although it is considered one of the greatest public works projects and civil engineering marvels of all time, there were many sacrifices made by the people of the watershed. Land was taken by eminent domain, and entire towns were relocated or simply lost to make way for the reservoirs. Today, to avoid the prohibitively expensive need for filtration, the NYC Department of Environmental Protection and the watershed towns have embarked on a wide variety of water quality protection strategies. These include the acquisition of sensitive watershed lands and conservation easements, new sewage treatment and sand/salt storage facilities, septic system rehabilitation, and the promotion of sustainable forestry and farming practices.