These New York waterways are clad in Prussian blue via the cyanotype printing process. Cyanotypes are more commonly seen in architectural blueprints, but they can lend an interesting effect to all kinds of scenes. Charles Gilbert Hine, like many amateur photographers of the period, likely chose the process for its relative simplicity and affordability.
Charles Gilbert Hine.
Cloud Study, [Sunset on water with ships in the distance], [Skyline at pier 14]. undated, 1883-1908. cyanotypes. New-York Historical Society.