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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.
Index of Biotic Integrity
Index of Biotic Integrity
How is this being measured?
Explanation of the grade
Key findings

B-Index of Biotic Integrity

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 Index of Biotic Integrity grade is primarily related to the clean aspect.

Guadalupe bass lays in hand palm.


The Index of Biotic Integrity (IBI) is designed as a way for River Authority Environmental Sciences Department (ESD) staff to sample, evaluate, and describe the condition of creeks and rivers throughout the basin. These metrics reflect fish species richness, trophic level composition (e.g., predators and omnivores), number and abundance of species, and condition of individual fish among other aspects of the overall fish community. These metrics are then combined and assessed based on a waterbody’s Designated Aquatic Life Use (ALU) as assigned by the Texas Commission on Environmental Quality (TCEQ) and Environmental Protection Agency (EPA), and can fall into one of five categories:  Minimal, Limited, Intermediate, High, and Exceptional. Theoretically, the less disturbed a stream is, the higher the IBI rating will be. River Authority biologists are constantly monitoring the San Antonio River Basin at numerous sites throughout the watershed to evaluate IBI. 

How is this being measured?

To determine the IBI grade for the 2022 San Antonio River Basin Report Card, we will use the last three years of data for each of the 17 sites monitored throughout the basin by the River Authority. Last year these metrics were calculated based on 20 sites. These measurements are done on a 3-year rolling average, and three sites that were assessed last year did not have data for the updated 3-year time frame. The River Authority adds or drops monitoring stations for a myriad of reasons including special studies based on watershed conditions starting or stopping, a more representative site is found within a waterbody, or site accessibility issues.

The grade will be determined by the number of sites meeting the designated ALU divided by the total number of sites monitored, multiplied by 100. Therefore, the grade for this metric is based on the percentage of monitored sites that meet the ALU designation.

Explanation of the grade

There are 11 of 17 sites achieving the associated ALU designation:

11/ 17 * 100 = 64.7%

Grade: B-

Key findings

This grade indicates that some of the creeks and rivers of the San Antonio River Basin have healthy fish communities. However, the score does indicate that further improvements can be made to enhance the diversity and abundance of these communities throughout the basin. Reducing disturbances to area creeks and rivers can help protect and enhance the health of their biotic communities. Healthy ecosystems are more resilient to existing disturbances and are characterized by high species diversity. A healthy San Antonio River Basin is a benefit not only for the aquatic communities that inhabit its waters, but it is also a valuable amenity for all residents of the basin.

Index of Biotic Integrity
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