Bristol Harbour is the harbour in the city of Bristol, England. The harbour covers an area of 70 acres (28 hectares). It is the former natural tidal river Avon through the city but was made into its current form in 1809 when the tide was prevented from going out permanently. A tidal by-pass was dug for 2 miles through the fields of Bedminster for the river, known as the "River Avon New Cut", "New Cut", or simply "The Cut". It is often called the Floating Harbour as the water level remains constant and it is not affected by the state of the tide on the river in the Avon Gorge, The New Cut or the natural river southeast of Temple Meads to its source.
Netham Lock at the east end of the 1809 Feeder Canal is the upstream limit of the floating harbour. Beyond the lock is a junction: on one arm the navigable River Avon continues upstream to Bath, and on the other arm is the tidal natural River Avon. The first 1 mile (1.6 kilometres) of the floating harbour, downstream from Netham Lock to Totterdown Basin, is an artificial canal known as the Feeder Canal, while the tidal River Avon follows its original route. Downstream of Totterdown Basin, the floating harbour occupies the former natural course of the River Avon, whilst the tidal River Avon flows through an artificial channel known as the New Cut. This separation of the floating harbour and the tidal River Avon allows boats in the harbour to remain floating at low tide, reduces currents and silting and prevents flooding.
Between Bristol Temple Meads railway station and Hotwells, the harbour and the River Avon run parallel at a distance of no more than 5⁄8 mile (1 kilometre) apart. Downstream of Bristol Temple Meads railway station, the floating harbour meanders through Bristol city centre, Canon's Marsh and Hotwells. At Hotwells, the floating harbour rejoins the tidal River Avon, via a series of locks, and flows into the Avon Gorge.
Bristol Harbour was the original Port of Bristol, but as ships and their cargo have increased in size, it has now largely been replaced by docks at Avonmouth and Portbury. These are located 7 mi (11 km) downstream at the mouth of the River Avon.