The River Nadder is one of the chalk stream rivers of southern England, much sought after by fly fishermen because of its clear waters and abundance of brown trout. It is one of the main tributaries of the River Avon, rising from a number of springs and small streams at Donhead St. Mary in south Wiltshire. The river winds its way east-northeast, heading towards the medieval cathedral city of Salisbury.
During the course of its 32 kilometre journey the Nadder meanders and widens gradually until it flows through the park of Wilton House to the west of Salisbury after which the river joins the River Wylye, another tributary of the Avon. For its last few kilometres it passes through the unspoilt water meadows at Harnham on the outskirts of the city, and finally into the River Avon beneath a backdrop of the magnificent Salisbury Cathedral spire.
The origin of the name is from Brythonic nootr, “flowing water”. Folk etymology derives it from the perceived likeness of its meanderings to an adder, the original Old English name for which was a nadder.