The Congress Avenue Bridge spans Town Lake in downtown Austin and is home to the largest urban bat colony in North America. The colony is estimated at 1.5 million Mexican free-tail bats. Each night from mid-March to November, the bats emerge from under the bridge at dusk to blanket the sky as they head out to forage for food. This event has become one of the most spectacular and unusual tourist attractions in Texas. The most spectacular bat flights are during hot, dry August nights, when multiple columns of bats emerge. There are several points from which to view the event, and an information kiosk is located on the north bank of the river, just east of the bridge. The Ann W. Richards Congress Avenue Bridge (formerly known simply as the Congress Avenue Bridge) crosses over Lady Bird Lake in Austin, Texas. Before the construction of Longhorn Dam was completed in 1960, the bridge crossed the Colorado River from which Lady Bird Lake is impounded. The bridge was known as the Congress Avenue Bridge from the construction of the first span across the Colorado River at that location in the late 19th century until November 16, 2006, when the Austin City Council renamed the current bridge in honor of the late Ann W. Richards, the 45th Governor of Texas and Austin resident. The bridge is a concrete arch bridge, with three southbound and three northbound vehicle lanes and sidewalks on both sides of the bridge. The bridge is currently home to the world's largest urban bat colony.