River Ouse Clarification: Not in Sussex—Two Major Ouse Rivers in UK

There is no River Ouse in Sussex. The question contains a geographic misconception. England has two distinct rivers named Ouse, neither flowing through Sussex:

1. River Great Ouse (East Anglia)

• Length: 230 km (143 mi) – UK's fourth longest
• Source: Near Brackley, Northamptonshire
• Course: Flows NE through Buckinghamshire, Bedfordshire, Cambridgeshire, Norfolk
• Mouth: The Wash (North Sea) at King's Lynn
• Key towns: Buckingham, Bedford, St. Neots, St. Ives, Ely, King's Lynn
• Significance: Major drainage for the Fens, navigation, water supply

2. River Ouse (Yorkshire)

• Length: 84 km (52 mi) from Ouse Gill Beck confluence
• Source: Formed by Ure + Ouse Gill Beck near Linton-on-Ouse
• Course: Flows SE through North Yorkshire
• Mouth: Joins Trent to form Humber Estuary
• Key towns: York, Selby, Goole
• Significance: Historic York's river, commercial navigation, flood management

Sussex's Actual Rivers

Sussex (East/West) is drained by south-flowing rivers to the English Channel:

• River Arun (longest wholly in Sussex, 60 km)
• River Adur (Shoreham-by-Sea)
• River Ouse (Sussex) – Wait—there IS a River Ouse in Sussex!

Correction: The Sussex Ouse

A third River Ouse exists in East Sussex:

• Length: 56 km (35 mi)
• Source: Near Lower Beeding, West Sussex
• Course: Flows SE through Lewes, reaches English Channel at Newhaven
• Significance: Lewes flood history, Newhaven port, South Downs chalk stream ecology

Answer: The Sussex Ouse is 56 km (35 miles) long. The confusion arises because "Ouse" (from Celtic usa "water") is a common British river name—at least five distinct UK rivers bear it.