The Collect Pond was essentially at the site of today's Columbus Park, just south of Canal Street, and it supplied the city's water until it became horribly polluted by the growing city in the 18th century. It's outlet had always been a marshy streamlet that ran west to the Hudson River, created a swampy area in the area now occupied by the western end of Canal Street, but the channel was dug out and straightened and became the namesake for Canal Street.
The Collect Pond in 1755, and below that the larger view of the map that this image was taken from:
The pond in 1766 (to the left is the triangle of City Hall Park):
And again in 1766, showing the line of the drainage canal and the surrounding marsh:
From the excellent site http://www.oldstreets.com:
Collect Pond: A large freshwater pond, irregular in shape, in the area roughly
bounded by today's Duane, Centre, Walker, Canal and Mulberry Streets,
and Cardinal Hayes Place. The name derives from the Dutch Kalck,
meaning chalk or lime, and probably refers to the piles of shells left
by Indians who had harvested oysters nearby. The name is also found
spelled Kolck, Kalk, etc. The pond was an important source of drinking
water in colonial times but became progressively more polluted. It was
filled in between 1802 and 1813. See also Five Points.