The lower part of the river is tidal; its original mouth was on the Wantsum Channel, an important sea route in medieval times.

The source, of what is known at that point as the Great Stour, is near the village of Lenham, within a short distance of the River Len, a tributary of the Medway.

Flood defences can turn this valley into a large lake and an embankment has had to be built to prevent overflow into the Medway catchment barely 100 metres (330 ft) away to the south.

Beyond Fordwich, the river passes between several former gravel pits and through the reed beds of the Stodmarsh National Nature Reserve.

Beyond the nature reserve lies the open farmland on the reclaimed marshes surrounding the river crossing at Grove Ferry Picnic Area, near the hamlet of Upstreet.

[2] At the hamlet of Plucks Gutter, the second of the large tributaries enters the main river: the 18.9 miles (30.4 km) long Little Stour, which begins life as a spring stream in Bekesbourne.

At this point the third large tributary, the 8.4-mile (13.4 km) Sarre Penn (named locally as the "Fishbourne Stream") enters with the Wantsum Channel.

Here the river turns southwards to the once-thriving port of Sandwich, after which it loops back on itself to the north before entering the Strait of Dover at Pegwell Bay.

During World War I, huge volumes of both troops and supplies were needed on the Continent and, in the utmost secrecy, a new port was built at Richborough.

Landing facilities along the Cut were built, and the East Kent Light Railway was extended to service the port.

[2] The Great Stour estuary at Plucks Gutter and Grove Ferry is renowned for its coarse fishing, particularly bream stocks.

[10][11] In 2017 The Marine Group based in Cardiff begun work with their water injection dredger on the river through Sandwich and Richborough to tackle some of the sediment build up.

Author Russell Hoban repurposes the River Stour where it flows through Canterbury as the "Rivver Sour" in his 1980, post apocalyptic novel Riddley Walker.