The Basha Kill lies in the valley between the Shawangunk Mountains and the Catskills, flowingsouth from about Summitville to join the Neversink River below the wetlands, and on to theDelaware River. The marsh was formed several times naturally as hurricanes washed debrisdown the Pine Kill, depositing it across the Basha Kill at Westbrookville.

The Bashakill Wetlands, a unique and biodiverse ecosystem in New York, faces significant ecological threats from invasive species, notably the Northern Snakehead. This predatory fish, originating from Asia, poses a severe risk to local aquatic habitats due to its aggressive nature and voracious appetite. The Northern Snakehead competes with native species for food and habitat, often preying on fish, amphibians, and even small birds and mammals, which can lead to a decline in native species populations.

The WMA has grown to include approximately 3,107 acres.In 1972, the State of New York through the Department of Environmental Conservation (DEC), purchased over 2,000 acres of wetland and adjoining upland to create the Bashakill Wildlife Management Area (WMA). When possible as additional properties around the wetland have come up for sale, the state has added more acreage to the Wildlife Management Area.