You may have seen this already but I recently read a great article in field and stream online called Going Deep in the Name of Trout Research. It discusses a subject that I've been interested in for a while, which is, what actually happens underwater. I think there is a lot of myth, legend, and misconception around what fish really do underwater, and how to catch them, based on their behavior. The only way to really clear it up is to get down there and watch it. These kinds of articles are worth their weight in gold.
This article has the author scuba diving while his partner is fishing. I won't restate the article. Check it out. It has some excellent insights.