The Haven is the tidal river of the port of Boston, Lincolnshire in England. It provides access for shipping between Boston Deeps in The Wash and the town, particularly, the dock. It also serves as the outfall into the sea of the River Witham and of several major land drains of the northern Fens of eastern England, which are known collectively as the Witham Navigable Drains.

Boston did not exist as a settlement prior to 1086, not being mentioned in Domesday Book. At the time, it was probably an un-named hamlet to the west of the larger settlement of Skirbeck, for which there were two churches recorded and two priests. One would have been St Nicholas's in Skirbeck itself, and the other was probably St Botolph's, by which name the early settlement at Boston became known. The settlement grew rapidly during the 11th, 12th and 13th centuries, as it lay between the city of Lincoln and the North Sea. Wool and corn were shipped down the River Witham, and Boston's location on an island of higher ground where the river joined a wide creek or haven made it an ideal site for a port.

Although the area to the north and west of Boston was a huge expanse of bog and marsh, the Haven was sufficiently shallow for it to have a ford. Two ancient trackways met there, one heading northwards to the Wolds, close to the route of the modern A16 road, while the other followed the coast, parts of which have been reused by the A52 road. The Wolds trackway ran along a slightly raised causeway called the "stick", and had been used in prehistoric and Roman times.

In the 12th century Boston and its Haven became busy with trade as wool was brought into the town for export, particularly to Flanders. A century later, the volume of wool exported exceeded that shipped from London. Other commodities included wheat, sea-salt, woollen cloth manufactured in Lincoln and Stamford, lead from Derbyshire and iron from Yorkshire. Imports included wine and finished cloth produced in the Low Countries from the wool that had been exported.

By around 1800, the lower reaches of The Haven had become of network of winding channels, increasingly plagued by deposits of sand and silt, which made the use of Boston as a port problematic. It also resulted in increased flooding within the town. Boston Corporation therefore asked John Rennie to suggest a solution for the 13.5 miles (21.7 km) of waterway from the Black Sluice to the sea. He proposed two solutions, the first of which involved straightening the channel between Skirbeck Church and the outfall of Hobhole Drain, from where a new cut would be created to reach the sea. The second was for a new cut from Skirbeck Church running to the north of the existing channel. The corporation chose the first option, which would shorten the distance to the sea by 4.5 miles (7.2 km). Work began in 1830 on an 800-yard (730 m) section above the Hobhole outfall. This reduced the length of the channel by 1.5 miles (2.4 km) and took three years to complete. Some of the channel was straightened by placing bundles of sticks known as fascines at outside bends. These resulted in silt being deposited on those bends, and the channel becoming straighter. Fascine work was carried out in 1841 and 1860. Silting of the river outfall became worse, and three Ruston steam navvies were used to create a new cut from Hobhole outfall to the Wash between 1880 and 1884.

Town Bridge prevented ships with masts from passing further upsteam, but river boats heading for Lincoln used the churchyard of St Botolphs as a quay. Once construction of the Grand Sluice was completed in 1766, they used a wharf above the sluice. On The Haven, boats used Packhouse Quay, subsequently known as Custom House Quay. To improve moorings, brick and stone walls were built on both banks of the river in 1815, from Assembly Rooms to Packhouse Quay on the east bank and at Doughty Quay on the west bank. Public warehouses were also built to serve both quays. However, by the 1880s ships resting on the mud at low tide was not particularly safe, and in parallel with the new channel to the Wash, a wet dock was built. All of the Victorian warehousing that was built has since been replaced by modern industrial units, as the port handles around one million tonnes of cargo each year.

The first ship to sail up the realigned channel and into the dock was the Myrtle, a 1,700-ton ship carrying cotton seed, which berthed in the dock on 20 December 1884. Development of the port had taken around 90 years, but resulted in a channel which scoured itself, needing little dredging. Land drainage in the area was also improved, as water levels on the downstream side of the Grand Sluice were reduced by around 4 feet (1.2 m).

Improvements to The Haven convinced a group of businessmen to set up the Boston Deep Sea Fishing and Ice Company in 1885. Initially they worked two new-build steam trawlers and seven sailing smacks, but gradually phased out the smacks, as the trawlers were more profitable. By 1890, they had 24 trawlers, and later amalgamated with the Boston Steam Fishing Company, another company which operated from The Haven. Fred Parkes, who had four boats of his own, joined the company in 1919. He wanted to replace older trawlers with new ones, but facing opposition, he waited until 1924, by which time he owned a controlling interest in the company. The new trawlers returned the company to profitability. In 1922, The Haven was blocked for three months when a coaster capsized. The company finally managed to salvage the sunken vessel, but Boston Corporation were unwilling to pay the recovery costs despite having agreed to do so. This together with a decline in the fishing industry led to the company moving its fleet to Fleetwood in Lancashire in 1923 and Boston declining as a fishing port.