"We could head back down to the lagoon."

"And do what? Sit out in the open? Next to a heavily used water source and hope that your captain decides to come back for you?"

"No, he won't do that he knows better. "

Ian Malcolm, Roland Tembo & Nick Van Owen(src)

The river that leads into the Lagoon.

The Isla Sorna Lagoon is an unseen area on Isla Sorna. It is mentioned by Ian Malcolm when his group and Ludlow's group try to decide how to call for a rescue. It is unknown where on the island the lagoon is located, but it is where the Mar Del Plata boat dropped off Dr. Ian Malcolm's team.