Xeric Ecoregion - National Lakes Assessment Results

• Key results
• Change from 2017

Key Results

An estimated 9,370 lakes in the Xeric ecoregion are represented in the National Lakes Assessment (NLA). Of these lakes, 38% are natural and 62% are man-made.

The NLA uses trophic state as an important indicator of lake condition and assesses the extent of biological condition and key stressors in the nation’s lakes.

• In the Xeric ecoregion, 41% of lakes are rated as hypereutrophic while 43% are eutrophic, 11% are mesotrophic and 5% are oligotrophic.
• The most widespread stressors assessed were nitrogen, and phosphorus with 81% of lakes in poor condition for nitrogen and 70% of lakes in poor condition for phosphorus.
• Cyanobacteria are one-celled photosynthetic organisms that normally occur at low levels. Under eutrophic conditions, cyanobacteria can multiply. Not all cyanobacterial blooms are toxic, but some may release toxins, such as microcystins. For information about risks at specific locations, recreational water users should check with state, tribal or local governments.
  • Based on microcystins, detections occurred in 71% of lakes and 25% of lakes were above the recreational benchmark.

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Change from 2017*

• For the Xeric ecoregion, the NLA reports that the percent of lakes with microcystin detections increased by 56 percentage points between 2017 and 2022.
• The percent of lakes that are in poor condition for chlorophyll a increased by 39%.

To access more ecoregional specific information, please visit the interactive NLA Dashboard.

* The change analysis is based on information from two points in time – 2017 and 2022.