Report Card Background Image

San Antonio River Basin Report Card 2022

San Antonio River Basin Report Card Summary
The overall grade for the 2022 San Antonio River Basin Report Card is B. This grade is the average of twelve individual indicator grades, which are explained in greater detail below.
Swimming Standard
Swimming Standard
How is this being measured?
Explanation of the grade
Key findings

D+Swimming Standard

Why is this important?

While all the metrics in the San Antonio River Basin Report Card have overlapping correlation to the safe, clean, enjoyable creeks and rivers aspects of the River Authority’s mission, the Swimming Standard grade is primarily related to the clean and enjoyable aspects.

The quality of life and health of citizens who live in the River Authority’s District can be improved through having recreational access along creeks and rivers. With more access, people can develop a greater appreciation for the natural resources and quality of life benefits provided by the San Antonio River and its tributaries. This appreciation will lead to an awareness of the issues affecting the river promoting increased preservation and conservation of these resources by individuals, businesses, and government.

Two children run through the San Pedro Creek splashpad.


The 4,194 square miles of watershed that feed the San Antonio River contain diverse sources of contaminants that may affect water quality in the river and its tributaries. Reducing these sources to achieve a water quality standard in the creeks and rivers that is consistently safe for direct human contact (i.e. recreation) would generate lasting and recognized improvements to the health of the overall basin.

To determine suitable recreation use, the River Authority measures Escherichia coli (E. coli) bacteria as an indicator of recent fecal contamination to area waterways. E. coli comes from the gut of warm-blooded animals, and while most strains are not typically harmful to humans, it is a measure of recent fecal contamination. Fecal matter may contain disease-causing bacteria, viruses, or protozoans. Typical sources of E. coli include wildlife, domestic animals, and humans. When it rains, E. coli levels in our creeks and rivers rise exponentially. This is because as it rains, stormwater runoff washes over the land, carrying fecal matter into nearby creeks and rivers.

How is this being measured?

San Antonio River Basin Watershed map


The River Authority has an extensive water quality monitoring program that compiles and reports data on a variety of contaminants in the water to the State. For this metric, the contaminant of importance is E. coli bacteria. The River Authority uses a geometric mean to determine the type of contact recreation at a given location. It is an average of water quality testing results over time. The geometric mean criterion for E. coli for the Primary Contact Recreation 1 Standard is less than or equal to 126 MPN (most probable number) per 100 mL. This regulatory surface water standard set by the Texas Commission on Environmental Quality (TCEQ) refers to activities which are presumed to involve a significant risk of water ingestion, such as swimming and wading by children. Thus, for the sake of simplicity in this basin report card, we have decided to use an informal name for this metric and will call it the Swimming Standard rather than using the formal regulatory name of Primary Contact Recreation 1 Standard.

Primary Contact Recreation 1 Standard


The grade for this metric uses the water quality monitoring data collected by the River Authority. The past five years of data is used to determine this grade by dividing the number of water quality monitoring sites that meet the Primary Contact Recreation 1 Standard by the total number of sites monitored in the basin and multiplying that number by 100. Therefore, the grade for this metric is based on the percentage of monitoring sites that meet the regulatory Primary Contact Recreation 1 Standard (i.e., Swimming Standard). It is important to note that 76 monitoring stations were identified last year (2020-2021) and 71 monitoring sites this year.

Explanation of the grade

Based on data from the River Authority’s Water Quality – Bacteria Dashboard there are 27 sites meeting the Primary Contact Recreation 1 Standard out of 71 total sites.

  • 27/71 x 100 = 38.0%

Grade: D+

Key findings

The data and corresponding basin report card grade indicate that E. coli bacteria levels monitored in the San Antonio River often exceed the state surface water quality geometric mean criterion for the Primary Contact Recreation 1 Standard. A deeper dive into the data shows that sites that have the most difficulty meeting water quality standards are located within urbanized Bexar County.

Primary Contact Standard

Annual rainfall rates also impact this report card grade. National Weather Service rainfall data for the last five fiscal years can be found here. (Note: The River Authority’s fiscal year runs from July 1 to June 30.) Years that have more rainfall are likely to have an increase in E. coli levels as bacteria levels tend to rise dramatically in the river following rain events, particularly in urbanized areas with large amounts of impervious cover. These high levels of bacteria have a significant impact when determining the geometric mean for the water quality standard.

It is not surprising that the water quality monitoring sites in urban areas have higher bacteria readings. As more natural surfaces are paved and developed, less water percolates into the ground and more water instead goes over impervious surfaces and into storm drains, picking up pollutants and carrying them to creeks and rivers. The untreated rainwater that goes into storm drains and directly to our creeks and rivers is known as stormwater runoff. The pollutants picked up by stormwater include, but are not limited to, oil, fertilizers, bacteria, heavy metals, gasoline, and sediment. Stormwater runoff (or non-point source pollution) is the most significant threat to water quality degradation in the San Antonio River Basin. It is also the most difficult to manage.

The problems associated with stormwater runoff are not confined solely to urban areas. Pollutants can negatively impact waterways when rain falls on farm and ranchland where fertilizers, animal feed, and animal wastes are not adequately buffered from creeks and rivers.

Report Card CTA Background



Find out more about sustainability and getting involved in helping protect your river, including watershed cleanup projects, building a rain garden, and much more.