40 Fathom Grotto is one of Florida's most famous naturally formed sinkholes

Name Dive Site:	40 Fathom Grotto
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World-famous 40 Fathom Grotto is a naturally formed sinkhole located in the heart of north-central Florida's thoroughbred racing country. It is the only place in the eastern United States where you can train, dive or play in depths of up to 200 feet or more. It's no wonder then that dive educators from around the world consider the Grotto to be the Ultimate Training Facility.

Geologically, the Grotto is what is known as an in-line sinkhole. Sinkholes form when the earth and rock above an underground river become weakened by the flow of water underneath. Eventually, this earth and rock collapses. Much of this material is carried away by the current; that which remains forms what is known as a debris cone, which the river now flows up and over.

Sinkholes seldom have perfectly straight walls (the Grotto is no exception). The Grotto's sides slope outward — often at a substantial angle — resulting in a diameter at the base which is several times greater than it is at the surface. Divers need to bear in mind that, even though they may appear to be in open water, ascents must be made cautiously — lest you clobber yourself on an overhanging ledge.

At this latitude, ground temperatures near the surface average 21°-22° C/72°-73° F; these are the temperatures one expects to find in most of the nearby springs. Temperatures at the Grotto, however, tend to be lower, ranging from 19°-20° C/68°-69° F at depth. This necessitates a minimum of a 6.5-7.0 mm wet suit a with hood; dry suits are all but essential at depths below 30 m/100 ft, and can substantially increase your enjoyment in shallower water.

Water flow can vary greatly at Florida's many natural springs. For example, due to their proximity to the Suwannee and Santa Fe Rivers, springs in nearby Gilchrist and Suwannee Counties can pump out millions of gallons of water a day. In contrast, groundwater flow here in Marion County is often barely detectable. This means that the visibility in the Grotto is subject to factors such as local rain fall and algae bloom. Fortunately, the Grotto is protected from the latter by a surface layer of duck weed, a chopped-salad-like plant growth that helps prevent sunlight from penetrating and, thus, inhibits algae growth.

Even though the duck weed performs a valuable function, no one really wants to emerge from a dive, covered from head to toe with hundreds of tiny green seeds. Nor do they have to. Mounted below the surface of the Grotto are a series of low-pressure bubbler vents. We turn these on before divers enter the water and, within minutes, the air bubbles create a large, duck-weed-free zone at the surface of the water.

Despite the presence of duck weed, visibility at the Grotto is generally not as good as one finds at surrounding dive sites, ranging from a normal high of 12 m/45 ft to, on rare occasions, a body's length or less. At many dive sites, this lack of stellar visibility would limit the property's commercial appeal. At the Grotto, however, it actually works to our benefit.

Over time, however, divers have managed to remove most of the junk, leaving only some venerable car wrecks. To this have been added an airplane, a motorcycle, a two-person tow sub and two different boat wrecks. For the careful observer, there are a number of Eocene-epoch fossils embedded in the natural limestone walls, including ancient sea biscuits and other invertebrates. (Your guide can point these out to you.) Among the Grotto’s most famous landmarks is this Suzuki motorcycle, suspended on cables at a depth of 40 feet. Divers can easily sit astride the motorcycle and pose for pictures. Perhaps the most whimsical addition to the Grotto is the Gnome City, a collection of miniature castles and people, located in a tiny cavern at 40 feet.

This information is distractred from www.40fathomgrotto.com. Visit 40FathomGrotto for more information, bookings and schedules.

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