Michael's swimming is better than the fish's!
I admired frogs' swimming so I frantically practiced the breaststroke until my arms and legs got longer.
I’m not very good at swimming.
This is the noun version of the kanji swim, so it means swimming.
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You learned this reading already so you should be able to read it!