How can I prevent a part from interacting with terrain?

Help and Feedback Scripting Support
#1

I’ve got this like 45 degree angle (water) that streches down quite a distance. And I’m trying to get these small balls to roll down the water, but instead they start rolling and get stopped and start floating in the water.

Any idea to solve this?

Example here: https://gyazo.com/33b736d33ea5c8686fdb071ce0384a7c

#2

Easiest solution I see here is to make a transparent part covering the surface of the water → make a collision group → set it so only the balls and floor can collide.