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Lake Austin - A TMDL Project for Dissolved Oxygen

A completed project to improve conditions for aquatic life by increasing dissolved oxygen in Lake Austin. Together, the adopted TMDL and the approved I-Plan are the road map to improving water quality.
photo of Lake Austin at Mansfield Dam

Lake Austin at Mansfield Dam
Photograph courtesy of the
Lower Colorado River Authority

County: Travis
Parameter: Dissolved oxygen
River Basin: Colorado River
Segment: 1411

Background and Goals

Low dissolved oxygen levels at the upper end of Lake Austin, immediately downstream of Mansfield Dam, led to the segment being listed as impaired for aquatic life use. The water released from the dam is low in dissolved oxygen because the releases are from the cold, noncirculating bottom zone characterized by oxygen depletion with no replenishment from circulation or photosynthesis. Since neither point-source nor nonpoint source loadings are causing the low levels of dissolved oxygen, this TMDL does not assign specific loads to pollutant sources. To address low dissolved oxygen in Lake Austin, the implementation plan calls for the use of an aerator at the dam to improve water quality to meet standards.

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TMDLs

The commission adopted this TMDL on November 17, 2000.

On December 5, 2001, the EPA recommended delisting the impairment rather than taking action on the TMDL, because it the cause of the low dissolved oxygen was pollution, not pollutants. The EPA stated that no official action is required for a TMDL written to address an impairment caused by pollution.

The letter from the EPA stated:

The U.S. Environmental Protection Agency (EPA), Region 6 received the Texas Natural Resource Conservation Commission’s (TNRCC’s) document entitled “A Total Maximum Daily Load for Dissolved Oxygen in Lake Austin (Segment 1403)” on December 13, 2000. Lake Austin is listed on the Texas 1998 Clean Water Act (CWA) Section 303(d) List for dissolved oxygen. However, according to the TMDL document, the cause of low dissolved oxygen in Lake Austin is due to pollution and not a pollutant. Specifically, the impairment is linked to the release of anoxic water into Lake Austin from the Mansfield Dam. Therefore, EPA recommends that TNRCC de-list the waterbody.

The TNRCC was the predecessor agency of the TCEQ.

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Implementation Plan

The commission approved the implementation plan on January 13, 2001.

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Contact Us

For more information, please e-mail us at tmdl@tceq.texas.gov and mention the Lake Austin project in the subject line. Or call us at 512-239-6682.

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