Scooby-Doo and the kids from Mystery, Inc. are taking a little vacation--they're going river rafting! But wherever the gang goes, a mystery is sure to follow. And soon enough the gang learns that a mysterious marsh monster has been scaring everyone away from the river. Now it's up to Scooby, Shaggy, Fred, Daphne, and Velma to unmask that monster-- before it ruins their summer vacation!