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National Lakes Assessment, Texas


To provide statistical analysis and probabilistic assessment of Texas lakes and reservoirs using data collected by the Texas Commission on Environmental Quality (TCEQ) for the U.S. Environmental Protection Agency's (EPA) National Lakes Assessment (NLA) project.

Study Area


Project Period

2013 – 2014


Texas has historically relied on targeted monitoring as the primary tool in evaluating the status of water quality in the state. This type of monitoring provides invaluable information about site-specific water quality issues. However, the data provided by targeted monitoring is of limited use in contributing to resolving large scale water quality issues such as:

  • What is the current range of water resources in Texas, and what is their geographic distribution?
  • What proportion of water resources is currently in acceptable ecological condition?
  • What proportions are degrading or improving, in what regions, and at what rates?
  • Are these changes correlated with environmental stress patterns and trends?
  • Are adversely affected resources improving in response to control and mitigation programs?
  • Are our water quality management strategies working?

These issues can only be resolved by applying a probability-based sampling approach with clearly defined resource populations. The EPA started using this approach in the late 1980s to evaluate water quality status and trends on a national level through the Environmental Monitoring and Assessment Program.

In 2007, TCEQ participated in the first NLA. Over 1,250 lakes and reservoirs were sampled across the continental United States.

The NLA's two main objectives are 1) to estimate the current status, trends, and changes in selected trophic, ecological, and recreational indicators of the condition of the nation's lakes with known statistical confidence; and 2) to seek associations between selected indicators of natural and anthropogenic stresses and indicators of ecological condition.

TCEQ SWQM staff sampled 42 reservoirs to collect sufficient data for a valid probabilistic assessment of Texas reservoirs. This data can be used to provide a statistically valid estimate of overall water quality condition in Texas reservoirs.

Project Sponsors

Related links

EPA: National Lakes Assessment

Final Report: National Lakes Assessment 2012: A Collaborative Survey of Lakes in the United States