Oh neat, that was going to be my guess. Usually when I'm mapping more rural waterways there's always some old ranch with a long-dammed up "[Ranch or Family Name] Lake" along the stream. This is probably the same!

A quick search did also find the Austin Travels Magazine still calling it that in more recent years: https://www.facebook.com/austintravelsmag/photos/a-blue-heron-perches-on-a-log-in-walsh-lake-along-the-new-3-mile-brushy-creek-no/1195145819283021/