That's what we're here for!
The volume fog trick for water is a little bit counter intuitive, since it's usually used for mist and dust, but the effect is exactly what you want for water. All you have to do is change the color.
If you want to really get an isometric-like viewpoint here, I'd say move your camera to between 60 and 70 degrees, move it way back, and reduce the field of view even further, something like 6 degrees. That will reduce the perspective even further, approaching an orthogonal viewpoint. Depending on the options you have in Bryce, you'll probably need to adjust your IBL sphere. Either increase its size to keep the camera inside it, make sure it's set to single-sided, or turn off its primary visibility.
You may also want to start thinking about adding some grunge textures, particularly to the green land and the mountains, just to break up the flat colors. Also, maybe hunt around for some farmland textures. I know someone here made some really nice ones a while back, but I'm not sure about the resolution and scale.
Bryan Ray, visual effects artist