Walnut Creek is approximately 23 miles in length and has a drainage area of 56.5 square miles. The stream runs north-south, crossing from the Central Texas Plateau eco-region on the western side of Austin to the Blackland Prairie on the eastern side of Austin. This large watershed was selected for study because it covers Austin’s heavily developed zone to the Northwest and then transitions to the quickly developing and ecologically distinct eastern portion of Travis County. Walnut Creek has perennial baseflow and many distinct ecological and historical highlights, making it one of Austin's most important watersheds. The Surface Water Team has been monitoring chemistry, biology and habitat on Walnut Creek since 1996 and at the end of 2008 will publish a comprehensive watershed report.