Hi, You need to dive into the material functions. I think it is in the AboveWaterRefraction function, there is a color parameter, dont remember the name now, but it is a red color, the darker you adjust red, the less translucent the water becomes. I think it is just not turned public in the blueprint and not added to the construction graph.
It is also easier to deal with the blueprint, if you make an instance out of the ocean material.