South San Gabriel River Condition Is A Dire Wakeup Call For Central Texas

The South San Gabriel River has recently experienced surface algae so thick that birds could walk across it.1 One local resident described the shallow river as “permanently ruined.” The culprit is the Liberty Hill South Fork Wastewater Treatment Plant, which recently expanded to dump 1.2 million gallons of treated sewage per day into the river.

Pristine Onion Creek could be the next victim of treated sewage discharge, as the City of Dripping Springs has requested a permit to dump nearly a million gallons a day into Onion Creek. The parallels between the fate of the South San Gabriel River and the future of Onion Creek and Barton Springs are uncanny and disturbing.

The South San Gabriel situation provides a harrowing glimpse of what could happen to other central Texas waterways, under current laws. It serves as a warning about what happens to the quality of our waterways and water supply when treated sewage is directly discharged. It also underscores the need for an alternate solution.

South San Gabriel Background

After the Liberty Hill South Fork Wastewater Treatment Plant received a wastewater discharge permit in 2006 from the Texas Commission for Environmental Quality (TCEQ), small algae blooms began being appearing in the South San Gabriel River. Liberty Hill ramped up their wastewater discharge to 400,000 gallons per day by 2013. In January 2018, the plant expanded and began discharging 1.2 million gallons/day into the South San Gabriel, leading to significant increases in algae. The plant has future plans to discharge up to 4 million gallons/day of treated sewage under their current TCEQ permit.2 The Liberty Hill plant has incurred numerous violations over the years, including excessive discharge levels of algae-producing Nitrogen and Phosphorous, and dangerous E Coli bacteria. The plant was cited for excess levels of Ammonia Nitrogen in both January and February of this year.

Local residents are understandably upset about the fouling of their once-clear river. Several of these residents provided comments to the TCEQ, expressing their concern about the plan in 2015, but the TCEQ granted an expanded wastewater discharge permit anyway. As a result of the latest algae bloom, the TCEQ is investigating the Liberty Hill plant, but local residents don’t think much will come of it. The problem is the current law; it allows for treated sewage to be dumped into Texas waterways, including those waterways that contribute water to our underground aquifers and wells.

The South San Gabriel River and Onion Creek: A Tale Of Two Waterways

The South San Gabriel River and Onion Creek are ecologically very similar. Both originate as clear streams in the Texas Hill Country, both have limestone beds and scenic banks, and both have modest flows, typically drying up during summer months. Importantly, the limestone beds of both waterways are permeable, allowing water from underground springs to flow into the waterways at certain spots, while in other places the flow is out, from waterway to aquifer.3 These leaks in the limestone beds mean that anything dumped into either waterway eventually ends up in the Trinity and Edwards Aquifers, which are primary sources of drinking water for millions of Texans.4

LEFT: South San Gabriel River 1/2 mile upstream from wastewater discharge point5
RIGHT: South San Gabriel River 2 miles downstream from wastewater discharge point6

Math Tells the Tale

A simple math analysis7 is all that’s required to understand why the South San Gabriel River became inundated with algae, and why the very same thing could happen to Onion Creek, Barton Creek, and Barton Springs. Nitrogen is one of the key elements present in treated sewage, and excessive amounts cause algae growth. The EPA states that once Nitrogen levels exceed 0.25 mg/liter in a waterway, algae growth (referred to as eutrophication) occurs.8 The treated sewage currently being discharged into the South San Gabriel,9 and that proposed for discharge into Onion Creek,10 has a Nitrogen level of at least 6 mg/liter, 24 times the eutrophication limit. This means that the natural flow of the waterway would need to be at least 24 times the flow of wastewater into it, to prevent excessive algae growth.

The South San Gabriel has an average (median) annual flow of 6.5 million gallons/day (mgd), while the Liberty Hill plant adds 1.2 mgd of wastewater. Thus the river flow is just over 5 times the wastewater flow, while it would need to be at least 24 times, to prevent eutrophication.

The proposed Dripping Springs discharge would go into Onion Creek, which has an average flow of only 5.2 mgd. The proposed permit would allow just under 1 mgd wastewater flow into Onion Creek, with only 5.2 mgd of average Onion Creek flow to offset it. The result would be heavy algae in the (formerly) pristine, picturesque creek. Because Onion Creek provides 30% of the flow into Barton Springs, the springs and Barton Creek would likely become fouled as well.

To make matters worse, the calculations above don’t take into account the background levels of Nitrogen already present in the waterways, before treated sewage is added. Since both the South San Gabriel River and Onion Creek already contain small amounts of Nitrogen, it would take even less wastewater inflow to cause eutrophication. Additionally, the actual average flow for both waterways is likely lower than stated above, since the measuring gages for both Onion Creek and the South San Gabriel are located several miles downstream from the wastewater discharge point. This means it will take even less wastewater discharge to cause algae growth.

No More Swimming and Fishing

Blooms of algae in surface waters are not only unsightly, but they also kill waterway ecology and recreation. Decomposing algae consume oxygen in the water, causing fish and other aquatic life to perish. Algae also restricts light from moving into the lower portions of the creek, altering habitat. These effects can reduce biodiversity even when a creek is not completely devoid of oxygen.

Recreation on the South San Gabriel has also come to a complete halt as a result of the recent massive algae blooms. “We had to get a pool, so the grandkids would have water to play in when they visit” says local resident Sharon Cassady. “I won’t let them swim in the river, it just isn’t safe.” Fishing has also disappeared on the South San Gabriel, with floating dead fish being frequently spotted by local residents.

A Health Risk

While it is unsightly, smelly, and slimy, green algae itself doesn’t propose a direct health threat. Drinking water tainted with treated sewage can be deadly, however. The permeable limestone beds on the bottom of Onion Creek and the South San Gabriel River can allow tainted water to flow into underground aquifers, resulting in well contamination. A recent study dropped dye into several parts of Onion Creek, and this dye wound up in seven Dripping Springs wells, due to the permeable limestone creek bed.11

At high levels, nitrogen is unsafe in drinking water, restricting transport of oxygen in the blood. This is especially dangerous for babies and young livestock. Additionally, treated effluent contains metals, cleaning products, pharmaceuticals including hormones, steroids, antidepressants, and many other harmful things people flush down their toilets. The effects of these products on humans are not fully known.

Treated wastewater also contains e-coli bacteria, which at even modest levels can cause life-threatening symptoms. System failures such as those seen at the Liberty Hill plant mean that discharged wastewater sometimes contains these dangerous pathogens.

There’s A Better Way

Surely there is a better way than using our creeks and rivers as open sewers. Treated sewage is dumped into waterways because it seems like the cheapest way to get rid of it; but what is the real cost? How much is a waterway like the South San Gabriel River or Onion Creek worth? How much enjoyment and revenue would be lost if Barton Springs closed due to excessive algae? How important is safe drinking water?

Land application of wastewater in Texas12 (left) and Pennsylvania13 (right)

The alternative to direct discharge is simple—use wastewater as a resource rather than a pollutant. Central Texas cities including Marble Falls and Lakeway do not discharge wastewater effluent. Instead, they utilize Land Application and Beneficial Reuse.

Land Application is simply applying the wastewater over a dedicated irrigation field, allowing the soil and plants to treat the wastewater. Beneficial Reuse uses effluent for watering public parks, augmenting industrial processes, and even flushing toilets. The City of Dripping Springs has recently proposed beneficial reuse for some of their wastewater, a positive development. There are many sustainable wastewater treatment technologies that are compatible with land application and beneficial reuse, including building and community-scale wastewater treatment.

As more people move to central Texas, the need for smart, sustainable solutions to our wastewater issues becomes of paramount importance. We can’t let the very thing that draws people here in the first place, our beautiful creeks and rivers, become ruined and abandoned like the South San Gabriel River. We can’t let development threaten our drinking water. A coalition of environmental groups has formed to promote a sustainable wastewater future for Texas. Learn more at, to assure a safe and enjoyable Texas for generations to come.


1 Austin American-Statesman

2 The Independent Liberty Hill

3 USGS Streamflow Gain-Loss Study

4 The Edwards Aquifer Website

5 Image capture from YouTube video

6 Image capture from Austin American-Statesman video

7 Projected Water Quality Degradation for Bear Creek at Ranch Road 1826 Resulting from Direct Discharge, by Raymond M. Slade, Jr., PH

8 EPA Limits – Slide 10

9 Liberty Hill TPDES Application summary

10 Dripping Springs TPDES Application

11 BSEACD Dye Study

12 City of Austin presentation image

13 Penn State University image