Day's Lock is the main gauging station for the measurement of the water flow in the River Thames.

It was judged best to build it on the Oxfordshire bank provided the existing weir owner would "remove his bucks"(eel traps).

A short way downstream of the lock is Little Wittenham Bridge which spans the river in two sections with an island between.

Using this, the lock is a short walk from Little Wittenham where is a car park near St Peter's Church.

Here it goes under Clifton Hampden Bridge and past the historic Barley Mow public house, as mentioned in the book, Three Men in a Boat.