How deep is Built-A-Raft River? The water in the Build-A-Raft River is 3 feet deep. Was this article helpful? Related articles Is the water heated in the Water Park? When is the best time to visit LEGOLAND Water Park? Can children who can’t swim ride the slides? Can I wear swim attire in the LEGOLAND Park? Is there an area to lay down towels and sit in the Water Park?