National Park Service

Sierra Nevada Network (SIEN)

Lake Monitoring

Sphinx Lake, Kings Canyon National Park Sphinx Lake, Kings Canyon National Park.

Lake Monitoring Briefs

Lake Monitoring Reports

Lake Protocol Documents


For more information contact: Andi Heard


Seeking Clarity: Tracking Change in Mountain Lakes

Importance & Issues

Sierra Nevada Network (SIEN) parks protect over 1,200 lakes that have some of the highest water quality in the Sierra Nevada. High-elevation lakes are critical components of the parks' ecosystems, popular visitor destinations, and habitat for aquatic and terrestrial organisms, including declining amphibian species.

Lake ecosystems were selected for monitoring because they are:

  1. Valued for their ecological importance, contribution to Wilderness character, recreational opportunities, and importance to regional water supplies.
  2. Threatened by multiple stressors.
  3. Sensitive to environmental change.

Despite their protected status within national parks, SIEN lakes are subjected to stressors that have the potential to adversely affect them. The stressors with greatest concern are air pollution (e.g., increased nutrient and acid inputs), climate change, non-native invasive species (e.g., fish), and localized visitor impacts. Sierra Nevada lakes are especially sensitive to changes from these stressors because the waters are very dilute and thus small changes can result in pronounced environmental effects.

Image of plastic corrals in Hamilton Lake in Sequoia National Park, part of a research project to study nutrient effects on water quality. Experiment in Sequoia National Park's Hamilton Lake to measure effects of different concentrations of nitrogen on algal growth. Photo by Andi Heard.

SIEN lake monitoring is designed to detect changes from multiple stressors, however, there is an emphasis on detecting effects from air quality. The Sierra Nevada parks are exposed to some of the worst air quality in the country. Nutrients, produced from agricultural, urban, and industrial sources in the San Francisco Bay Area and the Central Valley, are transported by air currents into the Sierra Nevada where they are deposited as wet or dry deposition. The parks are designated as Class I Airsheds under The Clean Air Act and Amendments, affording them the highest level of protection and prohibiting deterioration of air quality within the parks. Thus, the impacts from deposition of acids and nutrients are of high concern. Adverse effects from increased acid inputs include decreased ability to buffer further acid inputs and changes in biotic communities.


The other stressors with the greatest impacts on Sierra Nevada lakes are:

Human-induced Climate Change: Warming temperatures result in earlier snowmelt runoff, earlier ice-out on lakes, reduced summer base flows and soil moisture, a lower snowpack volume at mid-elevations, and increased flooding due to rain-on-snow events. These physical changes will have cascading effects on lake ecosystems.

Sierra Nevada yellow-legged frog Sierra Nevada yellow-legged frog. Photo by Bryan Czibeszky.

Non-native Species: The introduction of non-native fish to high-elevation lakes has resulted in precipitous declines in yellow-legged frog populations, as fish eat tadpoles, displace frogs from deep lakes critical to their winter survival, and fragment populations. The loss of yellow-legged frogs, a major predator of aquatic insects and a food source for alpine predators such as the western terrestrial garter snake, is likely to have measurable impact on the natural functioning of lakes within the frogs' historic range.

⇑ To Top of Page



Monitoring Objectives & Approach

The Sierra Nevada Network monitors water chemistry at a total of 76 randomly selected lakes: eight are sampled every year, and 68 are visited on a four-year rotation. Two additional index sites are sampled more than once in the summer/fall season to provide information on within-season variability in water chemistry. Amphibian surveys are conducted to provide information for park frog restoration projects.

Rafting out to collect mid-lake water samples in Kings Canyon National Park. Rafting out to collect mid-lake water samples in Kings Canyon National Park. NPS photo by Lyndsay Belt.

Monitoring objectives are:

  1. Detect long-term trends in lake water chemistry for Sierra Nevada Network lakes by measuring:
    • Temperature, pH, specific conductance, dissolved oxygen, acid neutralizing capacity
    • Major ions: calcium, sodium, magnesium, potassium, chloride, sulfate
    • A suite of nitrogen and phosphorous measures
    • Particulate carbon
  2. Detect long-term trends in lake trophic condition, using nutrient ratios as chemical indicators of trophic status.
  3. Characterize (the status of) Sierra Nevada Network lakes.
  4. Determine the proportion of Sierra Nevada Network lakes with chemical characteristics above/below threshold values for selected constituents.

More detailed information about why these metrics were selected for monitoring can be found in the Sierra Nevada Network Lake Monitoring Protocol (Heard et al. 2012).

⇑ To Top of Page

Management Applications

Outlet sample being taken at a Yosemite National Park lake. Collecting a water sample at a lake in Yosemite National Park. NPS photo by Dannique Aalbu.

Information from this monitoring project will:

  • Provide the parks with status information for network lakes. For example, this project will provide descriptive statistics and report on the proportion of lakes that exceed given thresholds.
  • Provide water quality trends for a suite of important indicators and measures.
  • Inform resource management planning and reporting efforts.
  • Provide managers with data needed to influence state and federal policy. Park managers can present information and work with agencies, such as California Air Resources Board and the Environmental Protection Agency, to influence policy (e.g., reducing non-point source emissions).
  • Assist managers in making informed decisions on the effects of emissions from industrial sources on park resources by providing scientifically credible long-term data.
  • Generate research questions and provide a rich data set that can be a spring board for research projects. A few examples of relevant research topics include critical nutrient loads, lake restoration efforts (i.e. fish removal), and effects of climate change and changing hydrologic regimes on lake processes.
  • Provide data to monitor compliance with state water quality standards.

Project Cooperators

Lake Monitoring brief

Lake monitoring in the Sierra Nevada Network parks resource brief
Click on image to download...

⇑ To Top of Page

Last Updated: December 30, 2016 Contact Webmaster