How do I use refraction to make underwater shadows look better? I'm using Cycles.

I've been messing around, trying to have fun with Minecraft Blocks in Blender. I also made water, using just a square - one face of a cube. I tried mixing transparent with diffuse BSDF, everything looks really cool, but I would like to have some refraction cause the shadows look unnatural.

I'll attach a photo so you know what I mean.

I don't know what to do. When I use Glass BSDF it looks like it's almost black.

Cheers.
Give the plane a single Refraction BSDF shader with blue color and IOR > 1.
Under Properties > Object > Ray Visibility uncheck shadow so the water does not produce shadow (that's why its almost black)