I had many fantastic wildlife encounters during my July 2018 trip to Key Largo, Florida. One of the best was the squadron of Spotted Eagle Rays that our diving group encountered near Permit Ledge on Molasses Reef.
Previous to this I had seen groups of 3 or 4 together but this was by far the largest squadron I have ever seen.
The spotted eagle ray is commonly observed in bays and over coral reefs as well as the occasional foray into estuarine habitats. Although it occurs in inshore waters to depths of approximately 200 feet (60 m), the spotted eagle ray spends most of its time swimming in schools in open water. In open waters, spotted eagle rays often form large schools and swim close to the surface.
The Florida Museum of Natural History website article (quoted above) about the Spotted Eagle Ray is one of the better sources of information that I have found.
I made another edit of the video where I focused and zoomed in on the last two rays in the squadron since they were a little closer to me. Notice that the last Eagle Ray is missing its tail.