ways." Due to tidal influence from the ocean extending to Troy, NY, freshwater discharge is only about per second on average. The mean fresh water discharge at the river's mouth in New York is approximately per second. The Hudson River is long, with depths of for the stretch south of the Federal Dam, dredged to maintain the river as a shipping route. Some sections there are around 160 feet deep, and the deepest part of the Hudson, known as "World's End" (between the US Military Academy and Constitution Island) has a depth of . The Hudson and its tributaries, notably the Mohawk River, drain an area of , the Hudson River Watershed. It covers much of New York, as well as parts of Connecticut, Massachusetts, New Jersey, and Vermont. Parts of the Hudson River form coves, such as Weehawken Cove in the towns of Hoboken and Weehawken in New Jersey. Salinity New York Harbor, between the Narrows and the George Washington Bridge, has a mix of fresh and ocean water, mixed by wind and tides to create an increasing gradient of salinity from the river's top to its bottom. This varies with season, weather, variation of water circulation, and other factors; snowmelt at winter's end increases the freshwater flow downstream. The salt line of the river varies from the north in Poughkeepsie to the south at Battery Park in New York City, though it usually lies near Newburgh. Geology The Hudson is sometimes called, in geological terms, a drowned river. The rising sea levels after the retreat of the Wisconsin glaciation, the most recent ice age, have resulted in a marine incursion that drowned the coastal plain and brought salt water well above the mouth of the river. The deeply eroded old riverbed beyond the current shoreline, Hudson Canyon, is a rich fishing area. The former riverbed is clearly delineated beneath the waters of the Atlantic Ocean, extending to the edge of the continental shelf. As a result of the glaciation and the rising sea levels, the lower half of the river is now a tidal estuary that occupies the Hudson Fjord. The fjord is estimated to have formed between 26,000 and 13,300 years ago. Along the river, the Palisades are of metamorphic basalt, or diabases, the Highlands are primarily granite and gneiss with intrusions, and from Beacon to Albany, shales and limestones, or mainly sedimentary rock. The Narrows were