Reduce FPS Overhead using Unity3D Pro Daylight Water

I’m using the daylight water (water3 - non wavey one, just dropping a Daylight Water prefab and scaling it to encompass my map which is a peninsula).

Using the profiler, I see this:

And it drops my FPS quite a bit, from around 120fps → 40fps - this is tested by running the profiler and enabling/disabling the water to see how fps rates are affected.

So my question is how can I prevent this from occuring? The water is “underneath” most of my map, is there a way to set an occlusion area to not include this water? or to tell unity to ignore water covered by terrain?

yes a occlusion area would be best
here is some information on it :