Water level monitoring for a pond?

I think I have a tiny little hole somewhere in my pond liner, and I’d like to start monitoring my water levels via HA to help diagnose where it is (but also just because it sounds fun).

Eventually, if I can figure out the hardware for this part, I’ll probably automate top offs via a cheapo B-hyve or something.

I was thinking about how a leak sensor may work for a binary “there is water/there is no water” setup where the sensor is at the bottom of the pond and alerts when it dries off, but that’s a bit too simple and also I’m not sure how long those can be submerged.

I’m at a loss on how to get the actual measurement for depth though. I have a 3d printer so I was thinking of printing a tube that stays anchored, and some sort of contact sensor in the middle that floats, but that’s feels like a dead end.

Anyone ever attempt something like this?