10. Mammoth – USA
Located at Holiday World & Splashin’ Safari in Indiana, Mammoth is officially the longest water coaster in the world. You ride in a big circular raft with up to 6 people as water jets push you uphill, then drop you down again — over and over. It’s a wild mix of speed, teamwork, and laughter. It’s like a water slide and a roller coaster had a baby — and it’s awesome.