noun
Refers to the act or skill of swimming. Often used in compounds like 泳ぎ方 (way of swimming) or 泳ぎに行く (go for a swim).
夏は毎日プールで泳ぎの練習をしている。
In summer I practice swimming at the pool every day.
彼の泳ぎはとても速い。
His swimming is very fast.
水泳 is a more formal or general term for swimming as a sport or activity, while 泳ぎ is a more casual, everyday noun often used in personal contexts.
The noun form of the verb 泳ぐ (およぐ, 'to swim'), derived from its continuative stem. The kanji 泳 carries the meaning of swimming.