The Eastern Narrows is generally shallow, but also has a natural channel. The tidal range is high, and flushing occurs between the East River and the Western Narrows, through the Eastern Narrows, but this water transfer is fairly inefficient. It has a muddy bottom and the sediments are highly contaminated from historical industrial activities. There are chronic dissolved oxygen problems in the bottom waters of the Eastern Narrows. The water is less turbid, and there is higher phytoplankton growth. The Eastern Narrows is densely suburban. There is a significant input of treated wastewater and urban stormwater to this area. The watershed draining into the Eastern Narrows includes primarily small coastal streams draining Long Island, Westchester County, NY, and Connecticut.
This reporting region extends from the Western Narrows to a line extending from Eatons Neck between Huntington Bay and Smithtown Bay on Long Island to Noroton Point between Fivemile River and Wilson Cove in Connecticut. The Eastern Narrows forms the northern boundaries of Hempstead Harbor, Oyster Bay, Oyster Harbor, Cold Spring Harbor, and Northport Bay on Long Island and the southern boundaries of Mamaroneck River, Milton Harbor, Greenwich Harbor, Indian Harbor, Cos Cob Harbor, Greenwich Cove, Stamford Harbor, Westcott Cove, Cove Harbor, Scott Cove and Fivemile River. There are numerous small islands along the Connecticut shoreline of the Eastern Narrows.