Swimming is a feature in Animal Crossing: New Leaf and Animal Crossing: New Horizons that allows players to swim in the sea and dive to catch sea creatures. While initially absent from Animal Crossing: New Horizons, swimming was added in the 1.3.0 Free Summer Update in July 2020.
In order to swim, players will need to obtain a Wet Suit. Once the player is wearing a Wet Suit, they can press A to enter the sea. They can either walk into the sea from the beach or jump off of the pier, a cliff (only in New Leaf), or beach rocks (only in New Horizons). Once in the water, players can swim faster by repeatedly tapping A, and they can dive underwater for up to eight to ten seconds by pressing Y. Once underwater, players can move around, and if they resurface while over a shadow, they will catch a sea creature.
Two players swimming while another is fishing in New Leaf
A player jumping into the sea from the beach in New Horizons
A spread from the Summer 2020 issue of Nintendo Magazine highlighting swimming