Peter Bluff: This is what I call a 'continuous' swim. You swim upstream but you don't make progress as the gentle current from the weir will hold an average swimmer in place. The river bed here is gravely, so pleasant underfoot and the normal Thames current here is invigorating.
Swim off the beach into the middle of the river. Turn and face up-river and swim against the normal downstream from Oxford current. It is the best, most delightful, exercise. Access.
At the bottom of the B4009 where it swings through the Western edge of Benson village, fork right and keep the Church on your right then in about 20 yards there is a dead stop junction Turn left towards Wallingford and almost immediately right into an unnamed road Follow this road to the left for about 200 yards until you come to a Thames Conservancy sign. Park here and walk through the gate. Once you've crossed the walkway over the southbound, downstream end of the Lock follow the footpath along the side of the Thames. There are two beaches just a few yards along the towpath.