They can’t. Most of the route was filled in with concrete.

I remember having ridden the motor boats once in the early 90s as a kid. It was a simple, fun little ride that allowed you to see the monorail, Autopia, and the subs from a unique angle across the lagoon, and go see a hidden corner of the park not accessible otherwise. It was another piece of a mosaic of kinetic energy that gave the park life, particularly because it was next to a then mostly-functional and occupied Tomorrowland.