Swamp Bones

From the introduction:

Populated with alligators and poisonous snakes, the swamps of Florida are filled with danger. Occasionally, people die in those swamps. However, no one expected a university research team to vanish while cataloging swamp plants. The local authorities are baffled, so it is up to the investigators to find out why five people vanished in the swamp and a sixth person was found deathly ill and half insane.

This adventure is designed for a small group of moderately experienced investigators. It is set in the 1990s, but can be modified for a different time period.