The source of the River Haddeo is head streams which form in the Brendon Hills and join near to Withiel Florey. In 1979 a dam was constructed to impound the river's water and Wimbleball Lake was formed. From Hartford, the site of the dam, the river flows west through Hartford Bottom and then south to join the River Exe a few miles south of Bury.
The valley of the river consists of three tributary valleys extending down from the surrounding farmland to merge with the River Haddeo in the south. The tributary valleys include the River Pulham, which passes the village of Brompton Regis and continues to Hartford where it joins the Haddeo.