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A total of 2,180 lakes in the Xeric ecoregion are represented in the NLA. Of these lakes, about 11% are natural and 89% are man-made.  

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

• In the Xeric ecoregion, 20% of lakes are rated as most disturbed based on trophic state, 30% are eutrophic, 27% are mesotrophic, and 22% are oligotrophic.
• The most widespread stressors assessed are phosphorus (39% of lakes), riparian vegetation cover (32%) and nitrogen (31%).

• Trophic State

  

• Indicator with the Highest Percentage of Lakes in the Most Disturbed Condition: Phosphorus

  

Human Use Condition: Cyanobacteria is one of three algal toxin related indicators presented in the NLA (see also chlorophyll a and microcystins). It serves as a proxy for the presence of algal toxins.

• Utah lake sampled during the NLA 2012. Photo: Ben Brown.Based on cyanobacteria cell counts, 16% of lakes in the Xeric ecoregion are in the most disturbed condition (i.e., pose a high risk of exposure to algal toxins).

Change from 2007 (for lakes >4 hectares)*:

• For the Xeric ecoregion, the NLA reports a 31% decrease in the proportion of lakes in most disturbed condition between 2007 and 2012 based on the condition of benthic macroinvertebrates.
• There was also a 17% decrease in the proportion of lakes in the most disturbed condition for both nitrogen and the lake drawdown exposure indicator.