How do you dive on Poptropica?

Big Nate island

You have to get a diving outfit. Catch the photo blowing by the left side of the lighthouse and swap it for the gear at the Say Cheese photo shop. Then you can dive for the lost lobster trap at Puffin Point.

Mythology Island

Go out into the water by the beach in Poseidon's realm. There is a dark area of water in front of the water statue, which leads to the underwater maze.