To be able to take nice underwater pictures from above, a small acrylic floating box will do so beautifully. Check the size of your smartphone and see if it fits the internal dimensions listed below. I'll be adding a list of known phones when I have their dimensions but it should fit a variety of smartphones including: Samsung, Android, LG, Sony, HTC, Nokia, Blackberry, Motorola, etc. Take pictures straight down, or take pictures through the clear side panel of livestock growing near the surface.
iPhone Users: Explore your reef for some ideal photographs, then place your iPhone in the Floater facing camera side down, screen side up. Tap the screen to focus on the subject, and tap the shutter button to take a picture while holding the box steady. If you'd prefer a remote switch to take pictures, plug in the Apple earbuds into the audio jack first. The volume control button will act as a remote shutter button to take pictures one by one as you click the switch with your other hand. The iPhone Floater has room for the plugged-in cable connection for remote shutter triggering.
Smartphone Floater dimensions: 8" x 4.5" x 3" (internally 7.5" long x 4" wide) This fits the iPhone 5, 6/6+, 7/7+, 8/8+, iPhone X, X Pro, and the newest iPhone 12, and a number of android phones.
Using a Spigen case on my iPhone there is plenty of space. The acrylic walls are 1/4" thick. If your phone uses an extra large case, double check the measurements above to make sure it will fit prior to ordering.