Vanishing Rocks is a very healthy shallow reef due to the currents that sweep through the passage between Cooper and Salt Islands. These currents, which when strong can make the site undivable, nurture its many species of corals and support a large population of reef fishes. The underwater ridge extends off to either side of the breaking pinnacle and is surrounded by lesser formations pockmarked with overhangs, ledges and undercuts. Descending from the boat will place you on a slope covered with gorgonians and small barrel sponges. Closer to the pinnacle there is a sandy area, surrounded by rocks and ledges. This is a great place to lie down on your belly, get your face in close and leisurely observe the inhabitants such as anemones and shrimp, jawfishes, and blennies. Thick delicate coral growth, lobsters, and occasional sleeping nurse sharks can be found here. Along the deeper water a little further out and you'll reach Sergeant Major City, a large multispired formation of pillar coral that is positively overflowing with fish life. Sergeant majors of course, but also squirrelfishes, grunts and bigeye snappers reside here. A little further along is an outlying pillar coral formation called, you guessed it, Sergeant Major Suburbs. Hugging the edge of the rock will bring you to a series of overhangs where a large green moray eel is often spotted.
Text extracted from The Guide to Diving and Snorkeling in the British Virgin Islands by Jeff Williams, Ria O'Hagan.