The River Thames is managed for Navigation from Lechlade, downstream to the sea, becoming tidal below Teddington Weir and Lock. Technically, Cricklade is the head of the navigation but few boats venture above Inglesham and the old junction of the river with the Thames and Severn Canal at the Round House (where there is no navigation authority).
The Thames is joined by the Oxford Canal via Sheepwash Channel and Duke's Cut at Oxford, by the river Kennet and the Kennet & Avon Canal at Reading and the River Wey Navigation at Shepperton. Other waterways join the tidal Thames.
The non-tidal Thames, from Cricklade Bridge (head of the Environment Agency's juridiction) is 135 miles long and has 45 locks, although with care, small boats can manage another 5 miles to Thames Head Bridge.
Teddington Lock is manned at all times. Other locks on the non-tidal Thames are manned by lockkeepers at certain times, and open for self-operation at other times.