Sea creatures are a new collectible in Animal Crossing: New Horizons following the first update. You can encounter them in the sea, and you need to dive into the ocean to find them. Before you jump into the ocean, you need to go swimming and dive into the water. You will need a particular item to do this, which you can purchase from the Nook’s Cranny, or grab one from the Nook Miles terminal.
The gear you want to purchase from the Nook Shop or the Nook Miles Terminal is the wet suit. You can find it available at the Nook Shop for 3,000 bells, or you can use 800 Nook Miles for the Nook Inc. themed one. After purchasing it, equip the wet suit from your inventory to wear it and approach the ocean on any side of your island. You won’t be able to jump into the river. While facing the sea, press the A button on your Nintendo Switch to enter the water.
To find sea creatures, you’re looking for bubbles in the water. You should see the slowly rising up to the surface, and when you approach the bubbles, press the Y button to dive down. While exploring the bottom, you want to direct your character to the dark shape in the water to grab it. You will then rise to the surface to show off what you found. There are 40 sea creatures available for you capture, and some of them seasonal.