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Satellite Monitoring (Secchi)

Monitoring Objectives

The monitoring objective is to assess lake water quality on approximately 8,000 lakes in Wisconsin by inferring water clarity from satellite imagery on an annual basis. This information is freely available to the public as well as the scientific community for understanding lake dynamics.

Monitoring Design

This effort has been built on a successful collaboration between UW-Madison, DNR and the Citizen Lakes Monitoring Network. Landsat satellite imagery is used in conjunction with citizen-collected Secchi depths to develop models that estimate water clarity in lakes 5 acres statewide. This DNR water quality monitoring activity, performed annually, now has almost 20 years of record. At least two summer water clarity values from within a 3-year period are averaged to determine lake trophic status.

Water Quality Indicators

Secchi depth and trophic state index are inferred from the Landsat imagery. These parameters are used in WisCALM assessments.

Quality Assurance

  • Field protocols and training
  • Data and image processing
  • SWIMS data flow QA checks
  • SWIMS data management checks

Data Management

All database records and image files are archived within the Monitoring Section. A file containing the Secchi estimates is sent annually to the SWIMS database management team and the data is submitted to the SWIMS database.


Generated data are summarized through the SWIMS database and the DNR's website where summary reports and graphs from SWIMS are available for downloading and review. These data are also summarized for the bi-annual Water Quality Report to Congress. The data is used for key parameter package analyses and statewide condition assessments.

Programmatic Evaluation

This DNR water quality monitoring activity is funded and evaluated annually. This effort has proven to be an extremely cost effective ($12,000 annually) and efficient method to produce a sizable database for the agency as well as the public and scientific community. In addition, General Purpose Revenue funded a project position from 2014 – 2017 that focused on this work.