In New York City, Buttermilk Channel is a small tidal strait in Upper New York Bay, approximately one mile long and one-fourth of a mile wide, separating Governors Island from Brooklyn. Origins of the name are mysterious but it is almost certainly a reference to the dairy farmers who used to cross this channel by boat to sell their milk in Manhattan markets. Some people believe that the channel got its name because crossing it was so rough that the farmers' milk was churned in to butter by the time they reached Manhattan. According to another legend, before the channel was dredged to accommodate cargo ships, cows were walked across it at low tide to graze on Governor's Island. In his newspaper articles about Brooklyn history, Walt Whitman wrote of a time "as late as the Revolutionary War (when) cattle were driven across from Brooklyn, over what is now Buttermilk Channel, to Governors Island. In the bitter volcanic winter of 1817— the volcanic winter following the "Year Without a Summer"— when the thermometer dropped to -26°F, the waters of the Upper Bay froze so hard that horse-drawn sleighs were driven across Buttermilk Channel to Governors Island.
In 1902 the channel was dredged extensively by the U.S. Army Corps of Engineers. With current charted depths of 35 to 40 feet, Buttermilk Channel is still a busy shipping lane offering the most convenient access to the Brooklyn waterfront. Its heavy use was historically connected to the Erie Basin terminal to the south and the Brooklyn Navy Yard on the East River. Most recently, large cruise ships and ocean liners, such as the Queen Mary 2, have been tying up at the Red Hook side of the channel, where the Brooklyn Cruise Terminal has been built.
The channel is marked by a number of navigation aids (green cans no. 5 and 7 at the NE entrance, and green gong no. 1, marking low water off the tip of Governors Island). Tidal currents on the channel are rather strong.