The channel at Pollock Rip Shoals is centered about 3miles east of the southerly end of Monomoy Island in Chatham, Massachusetts.[1] The channel, which runs east–west, is about 8miles south of the Chatham Lighthouse.[1] Vessels passing around the Cape Cod coastline use the channel as a passage from the Atlantic Ocean to Nantucket Sound.[1] The Pollock Rip Lightship marked the eastern approach to the channel from 1849 to 1969; it has since been replaced by a lighted buoy. The Stonehorse Lightship had previously identified the southeasterly end of the channel until October 1963, when it was removed by the U.S. Coast Guard and replaced with a small buoy.[1] The channel extends 6miles through the shoals and is deep and wide. It was completed in 1925.[1]