It rises at Seven Springs in Gloucestershire and flows south for approximately 37.3 km (23.2 mi) to meet the Thames at Cricklade in Wiltshire.

The name Churn is ancient, certainly pre-Roman and probably from a Celtic language, possibly that spoken by the Dobunni tribe, which controlled the area before the Roman conquest in the 1st century AD.

[7] Much of the catchment basin of the Churn was a key Roman settlement in the 2nd to 4th centuries AD, as Corinium Dobunnorum rose to likely status of capital of a division of Britain.

In 2006, the national government was engaged in a planning study to analyse methods of mitigating future flooding associated with the Churn.

There are several components that are used to determine this, including biological status, which looks at the quantity and varieties of invertebrates, angiosperms and fish.