WHat is the best ay to use Physical Materials with Character interaction?

Hey there,

im working on an frozen lake. The frozen Lake is begin blended out of 2 Material Layers that both come from 1 Master Material.

In the Frozen_Lake Material Instance, the being blended together. Id like to get a physical Material for the Ice, if the Lake is frozen, but not for the Water. Or maybe another*

How can i achieve this? The Character should walk on the ice and maybe slide a bit. Any Idea? THought about working with the Physical Material Map, but dont know how to seperate the both Layers.