There are 2 Blue Lagoon dolphin excursions.
The one we did back in June (our daughter is 7) was the "encounter". You are on a U-shaped, floating platform, and the dolphin swims up to interact with you. For one-on-one interaction, you stand or kneel on a platform that's underwater.
I don't know the title of the other one. For that, each person wears a life jacket and floats in the water with the dolphin. They then do different activities (swimming, etc.).
My daughter was in heaven to be able to touch a dolphin and have her picture taken with it!