I love this site Wild Swimming, a guide to Britain’s outdoor swimming places with lots of information on where to have a dip in rivers, lakes and coves with the help of a Wild Swimming map. The web also includes a section on the dangers of wild river swimming (slipping on rocks, hypothermia and cold-shock, jumping and diving, cramps and solo-swimming, weeds, blue–green algae, ‘swimmer’s itch’, Weil’s disease, fast water, currents, waterfalls, weirs) but put these into context:

About 400 people drown every year in the UK, but only a tiny percentage of these drown while outdoor swimming. An analysis of recent annual accident data shows that of the 12 per cent of drowning victims who died while actually swimming, 7 people drowned in swimming pools, 11 in the sea, tidal pools and estuaries, and 7 in rivers, lakes, reservoirs or canals. In addition there were 8 who died swimming drunk, 30 who died through ‘jumping in’ to water and 17 who died in ‘jumping and diving accidents’. 95 per cent of all swimming drowning victims were male and many were teenagers. More here