How could Reverse Mountain (One Piece) exist?

Question

In One Piece saga there is the so-called Reverse Mountain.

This is a Mountain with sea at east and west, land at north and south.

A river goes from east to west following the mountain. That means that stream goes upwards from east to the top of the mountain and downwards (as it should) from the top to west.

I wonder which kind of weird event could make such a river exist. It should be big enough to be navigable.

Edit: I expect it to have a natural river/mountain. Even though I realize that it might be almost impossible. In that case I feel acceptable to have a technological alternativa that is self-sustaining and uses nowadays technology at most.

Image to clarify.

Edit regarding the question duplicate: In the question it asks about why appears like stream goes upwards in maps. Actually the accepted answer explains how the water goes downwards but appears otherwise. This question asks about water really going against the gravity.

Answer 1

It might be a long, long open magnetohydrodynamic drive. Electric current in water, and magnets, may be electromagnets, can create substantial force.

Hard to do, dangerous and power hungry, but not impossible.

Answer 2

Water follows the path of least resistance. Gravity is an acceleration towards a (usually) specific point or area of mass.

Is gravity constant?

No, no it's not:

Geoid map of Earth.

Canada's missing gravity.

Having covered that, it is extremely unlikely that a mountain (more mass) would result in anything other than extra gravity. Unless, perhaps, it is hollow, made of very lightweight materials, and there is lots of missing mass underneath as well. But less gravity in the area alone isn't enough, you need a "downhill" gradient of gravity as well... at the top of the mountain.

Therefore, I conclude that while making a moderate amount of water flow uphill is a technologically trivial endeavor, making enough water flow uphill for it to be a navigable river, is not.

Not impossible if you can precisely control gravity, but I don't think water pressure alone will provide enough flow to not only counter gravity, but to counter the mass of the entire column of uphill water, sufficient to move a ship up an entire mountain. Or provide enough water in the channel to keep the ship afloat for the trip back down.

Answer 3

I have an idea which may well be impossible in real life and probably wouldn't look like a river.

How about a series of vents going up the mountain. Each vent would fire hot air pointed at the same angle as the mountain pushing the water up the mountain. The vents might have to be dug by hand to get the correct angles but they could be powered by geothermal energy making it self sufficient.