Everblue is an adventure game based around scuba diving. It is the predecessor to Everblue 2, and is the first of the Everblue series. It was released in Japan and Europe, but not in North America.
You play as Leo, a novice scuba diver, searching for treasure and learning about marine animal life. You are in a first person position - fighting off sharks, looking for treasure and watching beautiful scenery along the way.
Source: Wikipedia, "Everblue", available under the CC-BY-SA License.