The is carried by the current, and rushes forward on the water to slam straight into Hopper who's currently too preoccupied with the apparent faces in the water.

"What are you-" Henry begins, for he's managed to not spy any faces just yet; only the fact that Hopper's going to get slammed into by that desk, which will submerge him into the water if he topples over after — assuming he doesn't manage to stay upright, that is, which he very well might!

It's funny how habit works. Henry could very well just use his telekinesis to lift Hoppeer back on balance, but he reaches out a hand instead, instinctively. Having his powers tamped down for so many years, sometimes he still does things the hard way.