The River Parrett is a river that flows through the counties of Dorset and Somerset in South West England, from its source in the Thorney Mills springs in the hills around Chedington in Dorset. Flowing northwest through Somerset and the Somerset Levels to its mouth at Burnham-on-Sea, into the Bridgwater Bay nature reserve on the Bristol Channel, the Parrett and its tributaries drain an area of 660 square miles (1,700 km2) – about 50 per cent of Somerset's land area, with a population of 300,000.
The Parrett's main tributaries include the Rivers Tone, Isle, and Yeo, and the River Cary via the King's Sedgemoor Drain. The 37-mile (60 km) long river is tidal for 19 miles (31 km) up to Oath. Between Langport and Bridgwater, the river falls only 1 foot per mile (0.2 m/km), so it is prone to frequent flooding in winter and during high tides. Many approaches have been tried since at least the medieval period to reduce the incidence and effect of floods and to drain the surrounding fields.
In Anglo-Saxon times, the river formed a boundary between Wessex and Dumnonia. It later served the Port of Bridgwater and enabled cargoes to be transported inland. The arrival of the railways led to a decline in commercial shipping, and the only working docks are at Dunball. Human influence on the river has left a legacy of bridges and industrial artefacts. The Parrett along with its connected waterways and network of drains supports an ecosystem that includes several rare species of flora and fauna. The River Parrett Trail has been established along the banks of the river.

Quelle: Wikipedia