well, actually Bateman is not known for underwater paintings....but another is, and his name escapes me at the moment.
This gentleman actually puts on scuba equipment, and in addition to having assembled a decent photography resource for himself to work from, he paints in oils directly below, thus...like plein air, paints on location.
Bateman paints in transparent layers of acrylic color, but what Bateman has learned to do took him 20 years to develop, as did I or any number of artists.
You have to paint what you have some expertise of...as wildlife artists feel part artist and part the expert in their field as concerns biology and sciences. One must draw from the accumulated knowledge and experiences.
To paint well, underwater scenes...would require to become quite intimate with that environment. You need to project this intimacy to the viewer. Show us what in particular about the "deep" or shallows of freshwater bodies effects you the artist most deeply.
I won our state's Trout Inland stamp a couple years ago...and live in northeast Wisconsin. I and my son, have caught over 60 trout in the past month. The images in my heart and mind collectively come together to provide resources for new art works.
I am preparing to work on the Federal Duck stamp. I will draw upon years and years of duck hunting prior to about 15 years ago, all my sketches, photographs, some modeling with clay to establish poses, etc; You have to be so full of the environment, of the anatomical correctness of your subject of their relationship together, that your mind and artistic spirit is nearly bursting. Then..your works will be alive and rich. You will have something to say. It will be first most interesting to you, and then and only then interesting to the viewer...for instead of some stale illustration pose of wildlife, we will see the interpretation of your experiences.
(btw, nice to be back)