Book 27: Lost in the River of Grass by Ginny Rorby
Fourteen year old Sarah, who's on a swim scholarship at a private school, goes on a weekend field trip to the Everglades with a group of snotty, preppy kids and the likable, nice teacher. She finds herself faking sickness to avoid spending the day sloshing through the glades with the group and instead ventures out on an air boat with the fifteen year old son of the folks that run the camp.
What starts as a fun cruise through the cattails, saw grass, and marshy glades ends in a scary four day trek for the two teenagers as they try to get out of the glades on foot after the air boat sinks. With alligators, snakes, cuts and bruises, and a baby duckling, Sarah discovers she's more courageous than she ever thought and that she and Andy need each other in order to come out alive.