The river carries a heavy amount of silt, especially during the spring snow melt, from as far north as Quebec. The heavy silt concentration of the river forms a large sandbar near its mouth on Long Island Sound and has historically provided a formidable obstacle to navigation. The difficulty of navigation on the river is the primary reason that it is one of the few large rivers in the region without a major city near its mouth. The Connecticut River estuary and tidal wetlands complex is listed as one of the 1,759 wetlands of international importance under the Ramsar Convention on Wetlands.
The river's name is the French corruption of the Algonquian word "quinetucket" and means long tidal river. The first European to see the river was the Dutch explorer Adriaen Block in 1614. As a result of this exploration, the Dutch named the Connecticut River the "Fresh River", and it was the northeastern limits of the New Netherlands colony, and the original border between New Netherlands and New England. The first English colonist to record his visit was Edward Winslow from the Plymouth Colony in 1632. In 1633 the English built a trading post on the site of Windsor, Connecticut, and the Dutch built one with a fort at the site of Hartford, Connecticut. As the number of English colonists increased, the Dutch abandoned their enterprise in 1654. The Fort at Number 4, now Charlestown, New Hampshire, was the northernmost English settlement on the river until the end of the French and Indian War in 1763. In the Treaty of Paris (1783), ending the American Revolutionary War, the new border between New Hampshire and what was to become the Province of Canada was defined to include the "northwesternmost headwaters of the Connecticut" . Because there are several streams that could fit that description, a boundary dispute led to the short-lived Indian Stream Republic, which existed from 1832 to 1835.
At first the broad, fertile valley attracted agricultural colonies, but the volume and fall of the river contributed to the rise of manufacturing in the valley. The greatest single drop of is at Holyoke, Massachusetts. Other important centers include Windsor and Hartford in Connecticut, Springfield, Massachusetts, the largest city on the river, Lebanon, New Hampshire, and Brattleboro, Vermont.
In the late 1800s the river was used for massive logging drives from the far north, particularly the Nullhegan River basin in Essex County, Vermont. These spring drives were stopped after 1915, when pleasure boat owners complained about the hazards to navigation.
The Connecticut River Flood Control Compact was established in 1953 in response to severe flooding. The Clean Water Act in 1965 has also had a major impact on the Connecticut River and its tributaries; since then, the river has been restored from Class D to Class B. It was designated as one of the American Heritage Rivers in 1997. The towns along the lower end of the river have enacted a cap on further development along the banks, so that no buildings may be constructed except on existing foundations.
The mouth of the river up to Essex is thought to be the busiest stretch of waterway in Connecticut. Some local police departments and the state Environmental Conservation Police patrol the area a few times a week. Some towns keep boats available if needed.
The headwaters of the Connecticut River are at the northern tip of New Hampshire, near the Canadian border. Much of the beginning of the river's course in the town of Pittsburg is occupied by the Connecticut Lakes, a chain of deep, cold water lakes that are home to lake trout and landlocked salmon.
The river itself holds native brook trout, rainbow trout, large brown trout, shad, small-mouth bass, striped bass, carp, catfish, American eel, and several other species of game fish. Landlocked salmon make their way into the river during spring spawning runs of bait fish and during their fall spawn. The river has fly-fishing-only regulations on five miles (8 km) of river. Most of the river from Lake Francis south is open to lure and bait as well. Two tail-water dams provide cold river water for miles downstream making summer fishing on the Connecticut River excellent.
There is now a website which provides water-quality reports twice a week, indicating whether various portions of the river are safe for swimming, boating and fishing.
The Connecticut River is a significant barrier to travel between western and eastern New England. Several major transportation corridors cross the river including Amtrak's Northeast Corridor, Interstate 95 (Connecticut Turnpike) and Interstate 90 (Massachusetts Turnpike).