The lower half of the river is a tidal estuary, deeper than the body of water into which it flows, occupying the Hudson Fjord, an inlet that formed during the most recent period of North American glaciation, estimated at 26,000 to 13,300 years ago.

It had previously been observed by Italian explorer Giovanni da Verrazzano sailing for King Francis I of France in 1524, as he became the first European known to have entered the Upper New York Bay, but he considered the river to be an estuary.

In the nineteenth century, the area inspired the Hudson River School of landscape painting, an American pastoral style, as well as the concepts of environmentalism and wilderness.

The Hudson River was also the eastern outlet for the Erie Canal, which, when completed in 1825, became an important transportation artery for the early 19th century United States.

Pollution in the Hudson River increased in the 20th century, more acutely by mid-century, particularly with industrial contamination from polychlorinated biphenyls, also known by their acronym PCBs.

[7] USGS maps show the longest source of the Hudson as the Opalescent on the western slopes of Little Marcy Mountain,[32][33] originating two miles north of Lake Tear of the Clouds.

The Palisades are large, rocky cliffs along the west bank of the river; also known as Bergen Hill at their lower end in Hudson County.

Its outflow continues through the Narrows between Brooklyn and Staten Island, under the Verrazzano Bridge, and into Lower New York Bay and the Atlantic Ocean[31] through the Hudson Canyon.

This varies with season, weather, variation of water circulation, and other factors; snowmelt at winter's end increases the freshwater flow downstream.

[38] 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.

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.

[43] 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.

[44] 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.

A buildup of water in the Upper New York Bay eventually allowed the Hudson River to break through previous land mass that was connecting Staten Island and Brooklyn to form the Narrows as it exists today.

[45] Suspended sediments, mainly consisting of clays eroded from glacial deposits and organic particles, can be found in abundance in the river.

He then sailed upriver to a point near Stuyvesant (Old Kinderhook), and the ship’s boat with five members ventured to the vicinity of present-day Albany, reaching an end to navigation.

[50][51] The Dutch subsequently began to colonize the region, establishing the colony of New Netherland, including three major fur-trading outposts: New Amsterdam, Wiltwyck, and Fort Orange.

[52] The Dutch West India Company operated a monopoly on the region for roughly twenty years before other businessmen were allowed to set up their own ventures in the colony.

The works often juxtapose peaceful agriculture and the remaining wilderness, which was fast disappearing from the Hudson Valley just as it was coming to be appreciated for its qualities of ruggedness and sublimity.

[71] Their reverence for America's natural beauty was shared with contemporary American writers such as Henry David Thoreau and Ralph Waldo Emerson.

The line was built as an alternative to the New York and Harlem Railroad for travel to Albany, and as a way to ease the concerns of cities along the river.

[87] Emblematic of the increase in green development in the region, waterfront parks in cities like Kingston, Poughkeepsie, and Beacon were built, and several festivals are held annually.

[114][115][116] The Hudson River's sediments contain a significant array of pollutants, accumulated over decades from industrial waste discharges, sewage treatment plants, and urban runoff.

[6][117] Other kinds of pollution, including mercury contamination and discharges of partially treated sewage, have also caused ecological problems in the river.

[124] Zooplankton are abundant throughout both fresh and saltwater portions of the river, and provide a crucial food source for larval and juvenile fish.

[128][129] The hogchoker flatfish have been historically abundant in the river, where farmers would use them for inexpensive livestock feed, giving the fish its name.

Herman Melville, author of Moby-Dick, lived in and near Albany from 1830 to 1847, and was known to have ancestry from New Netherland, leading some to believe stories of the whale sighting inspired his novel.

[144] The New Tappan Zee Bridge between Westchester and Rockland counties has a pedestrian and bicycling path covering a distance of about 3.6 miles.

Another pedestrian and bike path exists further north, between Dutchess and Ulster Counties: Walkway Over the Hudson, which has a one-way length of 1.2 miles.

[38] The Hudson River can be canoed and kayaked for its entire length from Henderson Lake (GPS 44.091974, -74.057768) to the Atlantic Ocean at New York City.