Not far from where I live in Norfolk is the beautiful river Bure, and at Horstead mill the very big mill pool is very popular for jumping and swimming. There is a shallow stony area for paddling, deep mill pool, and a mill race to surf on. You can do longer deeper swims upstream. Also popular for kayaking and canoeing, with a brand-new platform in 2018 which doubles up as a swim entry point!
Grassy areas for picnics. Car park and parking on Mill Lane.
This is a crowd-sourced map. Abilities vary, and conditions change. Always assess risks for yourself before getting in.