Visible crew/equipment: After Calvin Bouchard makes the announcement to tourists visiting the Undersea Kingdom to evacuate, we see the tour guide lead the crowd through the tunnels. The green screen backdrop is still in the final cut. They forgot to add in the underwater effect.
Continuity mistake: When Dan walks down to a podium and looks over to see the dolphin knocking at the gate, the tee-shirt he is wearing changes from being plain white with a tag badge on his left, to a white shirt with a large blue stripe across it, with a tag badge being on the right. (00:08:20)
Revealing mistake: When the shark crashes in the control room and eats Fred, "Fred" is a dummy. His hand moves around in the water in an unnatural manner.
Answer: The lagoon was part of the theme park. Artificial with specific mammals inhabitants inside, warm and friendly.