Off Interstate 35 between Austin and San Antonio, Aquarena Center, as it is now called, was once the oldest amusement park west of the Mississippi River until Southwest Texas State University took over the 90-acre (36-hectare) property in 1994. The focus of the center has changed dramatically from entertainment to ecological preservation of the native plants and wildlife, including five endangered species.

Certified instructors must first complete the Aquarena Center's two-day Scientific Diver course before they can bring their classes to the designated scuba training area. The consistent 71-degree-Fahrenheit (22-degree-Celsius) water temperature, combined with great visibility and many varieties of fish, make the center an advantageous dive training site during the cold months of the year.

The spring waters were declared a "critical habitat" in 1980 and subject to the regulations of the Endangered Species Act. The area is also a registered archaeological site and is governed by the Texas antiquities laws. In 1996, an environmental review committee composed of federal, state and university representatives established the Scientific Diving Program to train all divers and coordinate all diving activities in Spring Lake.

The two-day course for certified divers covers a half day of classroom sessions on the geological, historical and biological aspects of the springs with emphasis on the antiquities and endangered species regulations as they pertain to divers. Buoyancy control skills are evaluated in the class at an underwater obstacle course where divers traverse through a series of hoops and grid cages without touching them. The divers also conduct hovering drills and transport a heavy object over another grid without a lift bag.

Since there are still glass-bottom boat tours, divers are trained not to surface while out on the lake to avoid contact with the boats.

The former underwater arena, where mermaids used to perform in front of the now-closed submarine theater, is the designated scuba training area. This area is separated from the rest of the lake by partitions and classified as a noncritical habitat. Certified instructors who have taken the Scientific Diver course can schedule with the center's scientific diver supervisor, Bridget Lewin, to bring student divers to the training area for open-water training dives. These divers are not allowed to venture beyond the training area.

Aquarena Center is operated by the Southwest Texas State University's Continuing Education Department's "Diving for Science" program. To find out more information about the program or to enroll in the Scientific Diver course, contact the scientific diving officer, Bridget Lewin, at (512) 245-9769 or go to the center's Web site at www.aquarenacenter.com. The cost of the Scientific Diver course is $200.