Every evening from March through October, the Congress Avenue Bridge in Austin releases the largest urban bat colony in North America—1.5 million Mexican free-tailed bats pouring into the Texas sky in a single darkening ribbon. The phenomenon began in 1980, when a bridge reconstruction created narrow crevices beneath the deck that proved ideal for maternal roosting. What locals first considered a nuisance is now the city's most-watched natural spectacle, drawing 140,000 visitors each summer and contributing an estimated twelve million dollars annually to the regional economy. Lady Bird Lake, the reservoir impounded by Longhorn Dam in 1960 and renamed in 2007 to honor the former First Lady's conservation legacy, provides the staging ground. The lake stretches five miles through the heart of downtown, its glassy surface reflecting the skyline's glass towers and the wooded bluffs that Lyndon B. Johnson once walked as a university student. Paddlers launch from docks along the Ann and Roy Butler Hike-and-Bike Trail, a ten-mile loop completed in 2014 that stitches together decades of piecemeal shoreline access. Water depth averages eight to twelve feet, the current negligible except after heavy rain, making the lake navigable for beginners and families. Austin sunset bat kayak tour departures cluster in the two hours before dusk, when light slants low across the water and the bats begin to stir. The bridge itself—a 1910 steel-truss span rebuilt in 1980—sits low and flat, its underside a forest of concrete expansion joints where guano accumulates in drifts and the air hums with echolocation clicks. Bat Conservation International, headquartered in Austin, maintains observation platforms on both banks and conducts nightly counts during peak season. The colony's emergence is timed to insect hatches over the Colorado River corridor; biologists estimate each bat consumes its body weight in moths, beetles, and mosquitoes nightly, a service valued at three million dollars in avoided agricultural pesticide use across Central Texas. The bats return to Mexico in late October, navigating by geomagnetic cues still incompletely understood, and the lake falls quiet until the scouts reappear the following March.