It is believed that the tour started after the events of The Lost World, which happened in 1997. By 1997, the public knew about the existence of dinosaurs on Isla Sorna.
Jurassic Park III
Ben Hildebrand and Eric Kirby took a tour of the island. As the boat enters a river basin on the island's edges, a large predator (likely the Spinosaurus) is heard jumping into the water, resulting in waves that hit the boat. Enrique instructs his driver to move the boat away from the noise as it enters a thick fog. When the boat emerges from the fog, both Enrique and his driver are gone, with the boat partially destroyed and smeared with blood. As a result of the unmanned craft crashing into nearby rocks in the shallows, Ben and Eric were forced to unhook themselves and land on the island.