The Wylye rises at Kilmington in the southwestern corner of Wiltshire and then disappears underground, reappearing at Coombe Barn, west of Kingston Deverill.[5] It then flows north through the Deverill Valley towards Warminster. From here it turns southeast to flow through the Wylye Valley, which skirts the southern edge of Salisbury Plain. At Wilton, the Wylye empties into the Nadder, which itself empties into the Avon at Salisbury. The Avon eventually drains into the English Channel at Christchurch.
The Wylye is fed by several winterbournes, which commonly dry up completely in the summer, so that the water flow in the river can vary greatly according to the time of year.[6]
The Environment Agency measures the water quality of the river systems in England. Each is given an overall ecological status, which may be one of five levels: high, good, moderate, poor and bad. 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. Chemical status, which compares the concentrations of various chemicals against known safe concentrations, is rated good or fail.[9]
