Specular reflections and diffuse media (fog) makes for massive render times though, in my experience. I did something similarish with water a long time ago, us

Specular reflections and diffuse media (fog) makes for massive render times though, in my experience. I did something similarish with water a long time ago, using a spectral renderer, finding spectral data for ocean water absorption and reflection, realistic spectral sun/sky model, and a physically-based ocean wave simulator to create the surface. The underwater "caustic god rays" looked very nice and realistic, and setting it all up was easy once I had found the data. But it took ages to get rid of the noise.