Lady Bird Lake (formerly Town Lake) is a reservoir on the Colorado River in downtown Austin, Texas, in the United States. The reservoir was formed in 1960 by the construction of Longhorn Dam at its eastern boundary by the City of Austin. The western end of the lake is bounded by Tom Miller Dam, built in 1939. The lake was created for several reasons, including the need for a cooling pond for the Holly Street Power Plant. The reservoir was also envisioned from the beginning as a recreational venue for the city. A system of hike and bike trails was built along the shoreline of the lake in the 1970s, establishing (what was then known as) Town Lake as a major recreational attraction for the city of Austin.

On July 26, 2007, the Austin City Council passed a resolution authorizing the renaming of the reservoir from Town Lake to Lady Bird Lake in honor of Lady Bird Johnson, the former First Lady of the United States and a long-time resident of the Austin area who had died earlier that month. Johnson had declined the honor of having the lake renamed for her during her life. In renaming the lake, the City Council recognized Johnson for her dedication to beautifying the lake and her efforts to create a recreational trail system around the lake's shoreline.

Lady Bird Lake is the easternmost lake of a chain of reservoirs on the Colorado River. This chain, known locally as the Texas Highland Lakes, also includes Lake Buchanan, Inks Lake, Lake LBJ, Lake Marble Falls, Lake Travis, and Lake Austin.