Every summer evening between March and November, 1.5 million Mexican free-tailed bats spiral out from beneath the Ann W. Richards Congress Avenue Bridge in a column visible for miles across Austin's skyline. The colony established itself in 1980, two years after the bridge's reconstruction left expansion joints wide enough to shelter nursing mothers; by 1982 the population had grown large enough to draw the first organized viewers. What began as a curiosity became North America's largest urban bat colony, a seasonal migration that attracts 140,000 visitors annually and contributes an estimated $10 million to the local economy through tourism and pest control. The bats' nightly departure occurs at civil twilight, typically twenty minutes after official sunset, when thermal currents lift insects over Lady Bird Lake and the Colorado River corridor. Observers on the bridge witness the spectacle from above; paddlers stationed two hundred meters upstream encounter the column at eye level as it fans east toward the Hill Country feeding grounds. The bats consume between 10,000 and 30,000 pounds of insects each night—primarily corn earworm moths, cutworms, and armyworm moths—making the colony one of the most economically significant pest-control agents in Central Texas agriculture. Lady Bird Lake, impounded in 1960 as Town Lake and renamed in 2007, stretches 6.5 kilometers through downtown Austin with a surface area of 468 acres. The waterway serves as the city's recreational spine, bordered by 16 kilometers of hike-and-bike trail and flanked by turtle habitats, heron rookeries, and limestone bluffs that predate the Balcones Fault escarpment. The Congress Avenue Bridge, completed in 1910 and rebuilt in 1980, spans 330 meters and carries 30,000 vehicles daily; its underside houses crevices 1.5 centimeters wide, the precise dimension that suits maternal roosting bats. Austin bat bridge kayak tour departures begin at 6:00 PM during peak season, timed to position paddlers beneath the bridge thirty minutes before emergence. Guided sunset experiences include naturalist commentary on echolocation, migration patterns, and the colony's role in regional ecosystems; tandem and single kayak rentals allow self-directed exploration upstream from the Auditorium Shores launch. The lake's average depth of 4.2 meters and absence of motorized traffic create stable paddling conditions; most tours cover 3.2 kilometers round-trip, returning after the final bats clear the roost.