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Upper San Marcos River: Watershed Protection Plan Implementation

Texas State University implemented management measures of the Upper San Marcos River Watershed Protection Plan, including hiring a watershed coordinator, installing demonstration NPS practices, conducting public outreach, reviewing local ordinances affecting water quality, and reviewing monitoring data for water quality trends.

Map of the Upper San Marcos River watershed with stream segments

Project Area

River Basin: Guadalupe

Water Body: Upper San Marcos River (1814)

Location: Hidalgo, Cameron, and Willacy counties


The Upper San Marcos River begins in the City of San Marcos at Spring Lake and flows 4.5 miles to its confluence with the Blanco River. In 2010, the Upper San Marcos River did not meet state water quality standards due to high concentrations of total dissolved solids (TDS) but has since met standards. The San Marcos Watershed Initiative, formed in 2012, guided stakeholders in the development of a watershed protection plan (WPP) to address the concerns for TDS, bacteria, nutrients, and sediment in the San Marcos River. They developed the Upper San Marcos Watershed Protection Plan (WPP) to mitigate future water quality issues in the watershed, which was accepted by the U.S. Environmental Protection Agency in 2018.

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Project Descriptions

August 2018 – August 2020

Texas State University implemented best management practices (BMPs) including low impact development (LID), aimed at managing the quantity and improving the quality of stormwater in the Upper San Marcos River watershed. LID was incorporated in new developments in the watershed and retrofitted into existing developments. This will encourage further implementation of BMPs and provide information on cost and effectiveness of BMPs in reducing pollution. Texas State also provided education and outreach, a review of water quality protection ordinances, and coordination of water quality monitoring activities.

June 2020 – February 2023

Windmill Branch flows into Sessom Creek, a tributary of the Upper San Marcos River. The Meadows Center revegetated the banks of Windmill Branch, restored riparian habitat, and implemented BMPs to reduce the amount of sediment that enters the water body and increase infiltration to groundwater.

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For More Information

Upper San Marcos WPP webpage

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

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