Thanks Lisa, It's a little tricky to find the underwater feature, but if it is the same Powershot I use it has a dial on top of the camera to switch camera modes. Turn the dial to select scene mode which will say SCN. then u can scroll through various scene modes, with the the selector button right beside the lcd screen, you will see different scenes like fireworks, beach, or foilage and also underwater. I think this mode works great for tank shots.