River Somer

The river rises at Chilcompton and flows to Midsomer Norton where it joins the Wellow Brook, which flows through Wellow and joins the Cam Brook at Midford to form Midford Brook before joining the River Avon close to the Dundas Aqueduct and the remains of the Somerset Coal Canal.
There is some debate as to the origin of the name "Midsomer". Different schools of thought include the difficulty in travelling to the area in times of flooding as opposed to the town's position at the branch of the river Somer. Eilert Ekwall wrote that the village "is said to be so called in allusion to the festival held at midsummer on the day of St. John, the patron saint." John Wesley wrote of the appalling local road conditions which ensured it was reachable "only in midsummer." As Simon Winchester notes in his book The Map that Changed the World, "...the roads on this part of Somerset were atrocious, thick with mud and as rough as the surface of the moon".

Wikipedia