Ok. Route18 is being built. There are water current. They are annoying when trying to scale. They will be even more annoying to try simulate, due to minecraft water physics.
If anyone would like to attempt a solution to these, feel free in the free build zone.
Until then, I shall mark out the currents with glass, and the jumpy bits with glowstone.
The route in progress:
Images of the current from the game guide: