Blend between cubemaps

Hey Guys,

I am creating a mobile game which uses a water shader that uses cubemaps for reflection.

As the new Standard shader is a bit too much for mobile, I was thinking of doing water reflections by blending between different cubemaps as the player moves down a river.

I don't know how to blend between cubemaps and was wondering if anyone could help. I can only swap cubemaps which is very noticeable. I'd appreciate your help. Thanks!