Exploring the Watershed

From the heights of Slide Mountain to the Esopus Creek valley, the Ashokan Watershed contains a diverse array of geographic features. An abundance of streams provide habitat for a variety of wildlife, many opportunities for outdoor recreation, and drinking water for nearly 10 million New York City and Hudson Valley residents. The Ashokan Watershed’s social and natural history make this area an endearing and special place to residents and visitors alike.

Social History  |  Creation of the Reservoir
Natural History | Geology  |  Physical Characteristics  |  Climate & Hydrology  | Land Use & Land Cover

Map of the Ashokan Watershed

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Social History of the Ashokan Watershed

The first inhabitants of the Ashokan Watershed were Native Americans of the Northeastern Woodland tribes. In the 1600’s, the Lenni Lenape of the Esopus Tribe living in the watershed by hunting and farming, began encountering Dutch settlers moving to the New World. Later, waves of immigrants seeking new opportunities joined the American melting pot. These new arrivals slowly pushed the Native peoples out of their ancestral land.

Following the Revolutionary War and the establishment of the United States government, the Ashokan Watershed area and much of the Catskill Mountain region became a center for resource extraction. Abundant hemlock trees provided tannin necessary for the tanning of leather products. Tanneries, charcoal kilns, and quarries sprung up along area streams and trade routes. The tannin and leather trade was so large that the Catskill Mountain region provided most of the leather goods to the Union Army during the Civil War.

In 1870 the railroad was built to Phoenicia, NY, providing a quick and easy way to bring goods to market, but by the late 19th Century most of the accessible hemlocks were cut, other resources had been exhausted and industries began leaving the area. With the railroad, however, came a growing summer tourist trade, and in 1904 the establishment of the Catskill Park permanently marked the region as a vacation destination. For much of the early 20th century, City residents traveled north to area boarding houses (many in close proximity to streams) to escape the brutal New York City summer heat and enjoy carefree days of fishing, hiking, camping, and other recreational activities.

Today, almost the entire watershed lies within the state-designated Catskill Park, a checkerboard of public and private land. As of 2012, the New York City Department of Environmental Protection owned about 11% of the land area in the Ashokan Watershed. Another 55% of the land area was estimated to be in public ownership, much of it within the Forest Preserve managed by the New York State Department of Environmental Conservation. Forest Preserve land cannot be sold or transferred without amending the state constitution.

The watershed contains several hamlets of relatively concentrated residential and commercial development, including the hamlets of Boiceville, Mount Tremper, Phoenicia, Shandaken, Big Indian, and Pine Hill. The Town of Shandaken has experienced a steady increase in population since the 1940s, reaching population levels equal to a previous population peak in the 1890s with the railroad and tannery industry boom.

The Ashokan Reservoir and the Creation of the New York City Watershed

By the late 19th Century, New York City had become a bustling port city, whose growing population had begun to overwhelm the City’s fresh water supply. Major droughts in 1895 and 1896 further stressed fresh water resources. Although the City had created a system of reservoirs in Westchester County, they were not adequate to supply its needs.

In 1905, after careful study and analysis, planners in New York decided that the Catskill Mountain region would be ideal for a new reservoir system. Using eminent domain, New York City acquired the properties of residents in the area that would become its new reservoir system. Some Catskill families lost their homes and believed that they were not compensated justly. Although hard feelings linger to this day, new partnerships are beginning to change that dynamic toward one of careful cooperation.

Work on the Ashokan Reservoir began in 1908 and was completed in 1915. The Esopus Creek was now broken into an upper and a lower part, with the Upper Esopus stretching from its headwaters at the top of Slide Mountain to the West Basin of the reservoir. The Schoharie Reservoir in Greene and Schoharie Counties was built between 1919 and 1928, as was the Shandaken Tunnel, which brought water from the Schoharie Reservoir to the Esopus Creek near Allaben to be delivered into the Ashokan Reservoir. The years to come would see the construction of additional reservoirs in Ulster, Sullivan and Delaware Counties.

The Ashokan is one of the largest reservoirs in the New York City water supply system. At the time of its construction, it was considered one of the wonders of the modern world — not only for the feat of engineering required to build the reservoir itself, but also the Catskill Aqueduct that brought the drinking water from the reservoir south over 163 miles of terrain to the Kensico Reservoir in Yonkers, NY. Consisting of two basins separated by a concrete dividing weir, the Ashokan Reservoir holds 122.9 billion gallons of water at full capacity. Including the water it receives from the Schoharie Reservoir, the Ashokan supplies approximately 40% of New York City’s daily drinking water needs in non-drought periods. The Esopus Creek enters the Ashokan’s West Basin and after a period of settling flows over a weir or is released into the East Basin. From the East Basin, water is released into the Catskill Aqueduct for drinking water use, or discharged via a release channel into the lower Esopus Creek. The reservoir’s drainage basin is 255 square miles, the large majority of which is represented by the towns of Olive, Shandaken, Woodstock, and Hurley in Ulster County, and Lexington and Hunter in Greene County.  Back to top

Natural History of the Ashokan Watershed


The entire Catskill Mountain region (which includes the Ashokan Watershed) was created by the interaction of water on rock. Much of its physical character today is a consequence of the most recent ice ages of 12,000 to 25,000 years ago when the Catskills were mostly occupied by glacial ice or the meltwater streams and lakes that followed the ice’s retreat. The mountains are composed of Devonian-aged sedimentary bedrock (sandstones, shales and conglomerate formed in ancient river valleys). Broken bits of this bedrock are the source of almost all of the stream sediment seen today — from clay to boulders. Cobbles and boulders in the streams have eroded from the thick-bedded sandstones that shape the mountain cliffs. The reddish, layered clays exposed in streambanks are ancient glacial lake sediments eroded from red siltstones and shales that form many of the mountain slopes. The nature of the glacial lake deposits and the dense, clay-rich glacial till that can form some channel boundaries makes them susceptible to stream erosion. Back to top

Physical Characteristics

The Ashokan Reservoir Watershed is 255 square miles in the south-central Catskill Mountain region and contains at least 459 miles of streams. The Ashokan Reservoir is primarily fed by the 330-mile Esopus Creek system draining about 75% of the watershed. Additional drainages include the Bushkill and smaller tributaries that feed directly into the Ashokan Reservoir. The Ashokan Watershed contains some of the most rugged terrain in the Catskills. Slide Mountain is the highest peak within the watershed at 4,180 ft. above sea level. The Ashokan Reservoir, by contrast, is 635 ft. above sea level.

Assessments throughout the watershed have shown that overall ecological and physical condition of streams is quite good. Closed-Canopy Floodplain Forest is the most common riparian cover type followed by Mowed Lawn with Trees (in the Esopus Creek watershed). A majority of banks along the Esopus Creek are bordered by more than 100 feet of riparian buffer. Fish and wildlife are abundant throughout the system, although habitat conditions diminish with distance downstream. Streams of the Ashokan Watershed are known for their trout fishery and supporting macroinvertebrate communities, but you may also find stream salamanders, green frog, snapping turtle, eastern painted turtle, wood turtle, and northern water snake in our stream corridors. Many bird species use the watershed’s streams, notably bald eagle, great blue heron, green heron, mallard, American black duck, wood duck, spotted sandpiper, belted kingfisher, bank swallow, and Louisiana waterthrush.

The trout fishery is sustained in part by cold water seeps in tributaries where spawning occurs. The Esopus Creek also receives flows augmented by releases from the Schoharie reservoir through an underground aqueduct, known as the Shandaken Tunnel. The Tunnel empties into the Esopus Creek through a portal located in the hamlet of Shandaken just west of Phoenicia. New York City is required to obtain a State Pollution Discharge Elimination System permit to regulate the allowable flow, temperature, and turbidity from the tunnel releases to protect trout and other organisms.

Stream conditions in the Esopus Creek downstream from the portal are characterized by cold water temperatures and high flow and turbidity during the summer. Cold water temperatures are beneficial to trout, while turbidity can be detrimental to the health of fish and other aquatic organisms, although little quantitative information exists for the impacts of turbidity on fish populations in the Esopus.

A study of brown trout response to temperature, turbidity, and flow regimes conducted during the summer of 2010 found that trout both above and below the aqueduct were stressed, with some indication of stress-refuge immediately downstream from the Shandaken Tunnel’s portal (Ross 2012). However, the study could not determine whether this refuge would benefit trout at the population level.

A second study conducted between 2009 and 2011 compared water quality, hydrology, temperature, and biological health of Esopus Creek (fish, macroinvertebrate and periphyton) communities upstream and downstream of the portal. The study concluded that though fish communities were altered at sites near and downstream from the portal, many changes were positive and could be related to changes in temperature or habitat quality and quantity (Baldigo et al. in prep). The only ecological impairment linked directly to the Shandaken Tunnel was a reduction in primary productivity at sites immediately downstream from the portal. Another potential adverse effect found was a significantly lower density of juvenile brown trout downstream of the portal. The authors noted that while these effects could be caused by impaired water quality, the aqueduct was only a minor contributor to turbidity and suspended sediment loads in the upper Esopus basin during the study period. In a separate study, researchers determined that seven tributaries and the last site upstream of the portal each contribute on average 2-10 times the amount of suspended sediment and turbidity to the upper basin than the portal did from 2010-11 (McHale and Siemion in prep).

Japanese knotweed, Didymo, and other invasive species are another ecological concern in the watershed. Water quality is very good in most portions of the watershed, excepting localized issues. Turbidity is the primary water quality concern, and is tied to the climate, geologic history, and stream management regime in the watershed. Although erosion of stream banks is localized (and generally not systemic), sections of eroding stream are threatening developed property and infrastructure and require management. Flooding and erosion are closely linked in the Ashokan Watershed. Large floods can initiate bank erosion. A recent increase in the frequency of large flood events and resulting channel adjustments may have exposed more of the system to erosion, at least temporarily. Source reduction efforts are focused on chronic sources, such as stream channel and adjacent hillslope erosion into glacial legacy sediments, and should over time reduce turbidity produced during moderate and low flows. Back to top

Climate and Hydrology

The southeastern Catskills with its high relief and high elevations captures a lot of water from humid air. When air is lifted up over a mountain range, the air expands, cooling and condensing into moisture, which takes the form of clouds and precipitation. The effect has been observed around Slide Mountain with a “bulls eye” of high annual rainfall, the highest on average in New York Sate. Historically winters in the area have left a snowpack in the mountains, and most large floods resulted from rain on snow melt, usually in the spring. However, the region is not immune to the destructive path of hurricanes and tropical storms, which generally occur in late summer and early fall. This was seen most recently with Tropical Storms Irene and Lee, which hit the area in August and September 2011. Although global climate forecasts can be difficult to scale down to local regions, it is expected that rainfall events with greater than one inch of precipitation are likely to increase in frequency and magnitude. Drought periods are also expected to become more extreme (in-between serious rain events), while snowpack amounts and duration are expected to decrease. As the frequency and magnitude of mid-sized storms increases, stream channels will likely enlarge to accommodate the larger flows until a new equilibrium is achieved. Channel enlargement could result in increased sediment loads (until the stream stabilizes) and more frequent shifts in channel alignments. Back to top

Land Use and Land Cover

Although forest covers over 95% of the watershed today, the 1800’s saw significant portions of the land cleared of forest by logging and bark peeling activity (for the tanning industry). Consequently, streams were altered from the increase in eroding sediment and the mostly deforested landscape. Along Route 28 (the watershed’s main thoroughfare) development associated with roads, residences, businesses, and town centers increases the amount of impervious surfaces. Farms were once common, but today there are no large-scale agricultural land uses in the watershed. Most farms and agricultural activities tend to be small with relatively low impacts on the landscape and environment.

For more information on these topics see the Esopus Creek Stream Management Plan.

Additional Resources:

Galusha, Diane. Liquid Assets: A History of New York City’s Water System. 1999, Purple Mountain Press: Fleischmanns, NY.
Social History  |  Creation of the Reservoir
Natural History | Geology  |  Physical Characteristics  |  Climate & Hydrology  | Land Use & Land Cover

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