Wiktionary
n. (context chiefly AU NZ English) An area for swimming in a stream or river.
WordNet
n. a small body of water (usually in a creek) that is deep enough to use for swimming
Wikipedia
A swimming hole is a place in a river, stream, creek, spring, or similar natural body of water, which is large enough and deep enough for a person to swim in. Common usage usually refers to fresh, moving water and thus not to oceans or lakes.
In the UK swimming at natural swimming holes has a long history and has recently become known as "wild swimming"., especially since the publication of bestselling books on the subject by Kate Rew and Daniel Start.
Nude swimming is a well-established tradition at some more remote swimming holes and is an attraction to many natural swimming fans.