There's a hidden chamber in my recent dungeon that's blocked by a waterfall coming from the ceiling and decending on a hole in front of the chamber. Right now, my players are cleaning the dungeon and just one of them suspects there's a hidden room behind that waterfall.

When they attempt to jump and move across it, should I give them disadvantage on the jump or take -3 points of strenght? I think disadvantage is kind of harsh, given that the hole is small in radius and that they're able jump across it without the liquid obstacle.

IRL the force of the waterfall would push them down the hole. How should I handle this?