The Great Bay Estuary, when counting the entire tidal system including the Piscataqua River, meets the Atlantic Ocean at the mouth of the Piscataqua, between New Castle, New Hampshire and Kittery, Maine. Tides carry salt water into the estuary twice daily from the Atlantic. Here it mingles with the fresh water influence from the various rivers that empty into Great Bay. It is one of the largest estuaries on the Atlantic Coast and at inland is one of the most recessed.