Aquarena Springs (Texas State University Aquarena Center)

The Texas State University Aquarena Center, located at 921 Aquarena Springs Drive in San Marcos, Texas, occupies the headwaters of the San Marcos River—one of the oldest continuously occupied sites in North America. Archaeological evidence indicates human presence at the springs dating back at least 12,000 years. The springs emerge from the Edwards Aquifer with such consistent force and temperature—approximately 70–72°F year-round—that the San Marcos River begins as one of the clearest rivers in the world, visible to its sandy limestone bottom throughout.

The centerpiece visitor experience is the glass-bottom boat tour, which departs regularly from the campus dock. Flat-bottomed fiberglass boats with glass viewing panels drift over the spring vents at depths of six to twelve feet, allowing clear observation of the underwater world. Texas blind salamanders—pale, eyeless, cave-adapted creatures that live entirely within the aquifer—are sometimes visible near the spring vents, as are hundreds of native fish species including the fountain darter, an endangered minnow found only in the San Marcos River system.

The spring lake and surrounding preserve are managed as aquatic wildlife habitat by Texas State University, which conducts ongoing research on the Edwards Aquifer ecosystem. Native aquatic plants including Texas wild rice—an endangered grass found only in this river—sway in the spring current visible through the boat's glass panels. Wading birds including great blue herons and snowy egrets nest in the cypress trees surrounding Spring Lake and are visible from the boat dock.

The San Marcos River below the Aquarena Center transitions into one of Texas's most popular tubing and kayaking rivers, with outfitters operating just downstream near Sewell Park. The combination of the spring-head glass-bottom boat experience and river tubing makes a full afternoon itinerary from a single location in San Marcos.