Underwater geocaches can be found in the waters of more than a dozen countries, from Indonesia to South Africa to Spain, but "there's just not that many of them out there right now," said Chris Waggoner, a veteran police officer from Gainesville, Florida, and an avid geocacher. About 100 geocaches around the world today require scuba gear, according to the Geocaching.com database, and just over half of them were listed in the past two years.

Geocaching is a hunt for a hidden "geocache", basically a container with a logbook. Some caches hold a trinket or treasure. The person who finds the treasure must sign the logbook and return the geocache to its original location. If you take something from the cache, you must leave something of equal or great value. Geocaching coins and so-called "travel bugs" (dog tags) have tracking codes on them, so they can be moved from cache to cache.

Scuba or underwater geocaching follows the same rules as the terrestrial-based game, but includes some challenges. Land-based geocaching uses GPS coordinates. With scuba / underwater geocaching, visual clues are added because it's difficult to give an exact GPS location on the water. The cache must also be submersible and must withstand water pressure and corrosion; logbooks are waterproof.

Geocaching experiences are shared online on sites such as Geocaching.com or OpenCaching.com run by Garmin, which makes GPS devices. Clues and rating systems are added, including the level of difficulty in finding the cache. For example, does the hunt require (for land hunts) biking or mountain climbing, or special scuba diving equipment (for water-based hunts)?

Geocaching is not regulated beyond what is approved by the community or volunteer reviewers on geocaching sites. Guidelines require permission before placing a cache on private property or on protected federal lands, and caches cannot be buried. There's no age requirement, so families can go hunting together.

There is no record of accidents or deaths associated with underwater geocaching. But there have been deaths among land-based geocachers from things like heart attacks and falls.

Scuba Diving / Underwater geocaching is one part of a big hobby, and geocaching overall is growing. Geocaching.com started in 2000 with 75 caches worldwide and now lists more than 1.6 million caches.

by Suzette LaBoy