Watershed Facts

• Onion Creek flows throughout the year with the creek beginning north of Dripping Springs and emptying into the Colorado River approximately eight miles downstream of Town Lake.
• The Onion Creek watershed passes through the environmentally sensitive Edwards Aquifer Recharge Zone where water travels through caves and sinkholes to “recharge” the aquifer.
• Onion Creek watershed is coming under increasing development pressure in both the upper and lower watershed. The upper end is primarily residential/rural based, while the lower end is associated with Austin/Bergstrom International Airport
• Onion Creek watershed is estimated to recharge nearly half of all water entering the aquifer and its recharge benefits all aquifer users between Onion Creek and Barton Springs.
• The City of Austin has purchased tracts that are responsible for almost one-third of Onion Creek Recharge in order to better protect the aquifer.
• Antioch Cave, located in the watershed, may have the greatest capacity to recharge water into the aquifer than any other known recharge feature.
• Dye tracing indicates that water moves at different rates through the aquifer depending on water levels. Dyes from Onion Creek have reached Barton Springs in as little as three days or as long as three weeks.
• In response to citizen calls, investigators find an average of 16 spills each year; the most common spill type is petroleum, followed by trash, then sewage.
• “Sea Monster found on Onion Creek by two UT Geology students” headlines in newspaper in 1935, was actually the “Mosasaurus” currently residing in the Texas Memorial Museum.
• Severe flooding is possible, especially in the lower end of the watershed.
  

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Creek Assessments
Environmental

• Benthic macroinvertebrate data indicate that Onion Creek is of high aquatic life use by state evaluation methods; presence of pollution-intolerant diatom species suggest healthy community.
• Lower portion of watershed threatened by erosion due to development pressure beyond City of Austin jurisdiction.
• Portions of Onion Creek are listed on the State 303(d) List of Impaired Waterbodies for depressed Dissolved Oxygen.
• The US Corps of Engineers is planning projects for flood and ecosystem restoration; this may result in federal funding for projects that improve water quality and aquatic life.

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Environmental scores are based on a full range of chemical, biological, and physical assessments.

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Photo Gallery
Onion Creek at McKinney Falls below lower falls	Onion Creek at Sky Ranch
Onion Creek at South Austin Regional wastewater treatment plant	Onion creek above IH35
Onion Creek near Driftwood, Hwy 150

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