You can swim practically from any shore to which there is public access.
Listed here are places which are popular and which we have visited.

Millerground, Lake Windermere
Just west of Windermere town. From Bowness take the A592 north, past the Steamboat Museum and into a Park and Ride car park. Follow the footpath to the lake. Beware of boats heading for the public landing stages. Stay within the marked area or risk being mowed down by very fast motor craft.
Another reported popular place is Red Nab at Windermere.

Coniston Water
There are many beautiful beaches and quality swims along the East side of the lake. Look out for weeds. Stay close to the shore to avoid boats. Beware of fast cars along the narrow road.
Galleny Force [see picture]
Described in the Sunday Times (24/7/05) as 'two magical shallow river pools by Gelleny Force' these are hidden away at the head of Borrodale. From Stonethwaite walk a few hundred yards up Langstrath Beck past a small island to find the lower pool.

Crummock and Buttermere are small unintimidating lakes with accessible shorelines for wild swimmers. Motor-boat free, 'they taste all the sweeter for it', says Simon Murie, founder of Swimtrek Swimming Adventure Holidays. 'I'd recommend combining either lake with a visit to Scale Force, the highest waterfalls in the Lakes: you can rejuvenate yourself underneath its flow.' (Observer 30/7/06)