Completed Total Maximum Daily Loads and Implementation Plans

Below is a list of completed Total Maximum Daily Loads (TMDLs) and Implementation Plans (I-Plans), with dates of adoption and approval by the commission and EPA.

Completed TMDLs and I-Plans

Download this spreadsheet for the latest detail on TMDL projects.

Microsoft Excel Document TMDL Summary Table (last updated August 16, 2024)

How TMDLs Are Counted

EPA requires one TMDL for each impairment listed in a water body. An impairment is the combination of the use that is affected (such as support of aquatic life) with the pollutant or condition of concern (such as mercury or low dissolved oxygen). For example, if Jones Creek was listed as not meeting the aquatic life use because of low dissolved oxygen concentrations, and not meeting the fish consumption use because of mercury in fish tissue, two TMDLs would be required for Jones Creek.

Prior to 2008, the number of impairments was reported by water-quality segment, as required by EPA guidance. During that period, TCEQ used the term “water body” synonymously with “water-quality segment” when reporting how many segments were addressed by TMDLs.

In 2008, EPA began requiring TCEQ to develop and record one impairment (and TMDL) for each assessment unit within a water-quality segment. Consequently, TCEQ reports multiple TMDLs (impairments) where once it would have counted only one. TCEQ continues to report the number of water bodies addressed through TMDLs by water-quality segment.

A water-quality segment is a geographic portion of a river, lake, or bay that has relatively homogeneous chemical, physical, and hydrological characteristics. A segment is assigned a unique number for the purpose of categorization and provides a basic unit for managing water quality. In some cases, a segment may be the same as the entirety of the water body; for example, a small lake may not be divided into multiple numbered segments.

An assessment unit is a further geographic subdivision of a segment. For example, Segment 0200 may have five assessment units.

Projects Develop Multiple TMDLs

To be most efficient with resources of time and money, the TMDL Program may address the same pollutant in multiple water bodies through a single project, or may address multiple similar pollutants (such as three different pesticides) in one segment through a single project. Hence, a single project may produce many TMDLs.

Federal law requires that EPA take formal action to approve or disapprove any TMDLs adopted by the states. So, on any particular date, the number of TMDLs adopted by the Commission may differ from the number approved by EPA.

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