Western Mountains Ecoregion - National Lakes Assessment Results
Key Results
An estimated 17,770 lakes in the Western Mountains ecoregion are represented in the National Lakes Assessment (NLA). Of these lakes, 78% are natural and 24% 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 Western Mountains, 2% of lakes are rated as hypereutrophic while 13% are eutrophic, 41% are mesotrophic and 44% are oligotrophic.
- The most widespread stressors assessed are nitrogen, phosphorus, and degraded riparian vegetation cover with 25%, 15% and 15% of lakes in poor condition respectively.
- 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 3% of lakes and no lakes are above the recreational benchmark.
Change from 2012*
- For the Western Mountains, the NLA reports that the percent of lakes in good condition for zooplankton decreased by 18 percentage points between 2012 and 2017 and the percent of lakes in good condition for phosphorus increased by 14%.
- The percent of lakes that are in poor condition increased by 15% and 9 percentage points respectively for chlorophyll a and riparian vegetation cover between 2012 and 2017.
To access more ecoregional specific information, please visit the interactive NLA Dashboard.
* The change analysis is based on information from two points in time – 2012 and 2017.
![Image showing the dashboard results from the NLA Interactive Dashboard](/system/files/styles/large/private/images/2022-06/WMT%202017%20Good.png?itok=V5cgM5GT)