This image of the Croton Reservoir in Central Park is from a stereoview, taken as part of Deloss Barnum’s “Views in Central Park” series. Barnum, who during his career was referred to by several variant names, was a photographer in Boston and New York in the mid-19th century. This rare stereoview is currently for sale on eBay, and the seller has graciously allowed us to use these images.
See here for an exquisite 1865 map of Central Park showing the a bird’s-eye view of the reservoir—today the site of the Great Lawn.
The New York Public Library has an online collection of other images in this series.