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Mission and Aransas Rivers Watershed: Total Maximum Daily Load Implementation

The Texas Water Resources Institute gathered additional water quality data to help prioritize activities in the Total Maximum Daily Load Implementation Plan for reducing bacteria in the Mission and Aransas Rivers.

Map of the Mission and Aransas Rivers watershed with stream segments

Project Area

River Basin: San Antonio-Nueces Coastal

Water Bodies: Mission River (2001, 2002) and Aransas River (2003, 2004)

Location: Bee, Goliad, Karnes, Refugio, and San Patricio counties


Since 2004 multiple segments in the Mission and Aransas River watersheds have not met all water quality standards because bacteria concentrations exceeded the criteria used to evaluate attainment of the primary contact recreation use, and also have concerns for depressed dissolved oxygen. Portions of the Aransas River have also had concerns for excess nutrients. In 2016, a Total Maximum Daily Load (TMDL) Implementation Plan (I-Plan) was finalized for these two watersheds. TMDL I-Plans are developed in coordination with watershed stakeholders with the goal of mitigating sources of pollution and restoring full use of the water body. Stakeholders decided that the gathering of additional water quality data was necessary to inform the selection of implementation measures.

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Project Description

The Texas Water Resources Institute (TWRI) conducted monthly routine monitoring at three stations (two on the Aransas River and one on the Mission River) that complemented an existing routine quarterly monitoring conducted through the Clean Rivers Program.

TWRI collected near-surface water samples and analyzed them for bacteria, total suspended solids, turbidity, nitrate-nitrogen, ammonia nitrogen, total Kjeldahl nitrogen, and total phosphorus. They also recorded field parameters including pH, temperature, conductivity, and dissolved oxygen. TWRI maintained a database for these water quality data and submitted them to the TCEQ Surface Water Quality Monitoring Information System. The project was completed in August 2020. Data will be used for assessment purposes and to track water quality improvements from future TMDL implementation efforts.

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For More Information

Mission and Aransas Rivers TMDL.

To find out more about the NPS Program, call 512-239-6682 or email us at

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