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Lakes Health

Satellite Monitoring - Secchi

Monitoring Objectives

The monitoring objective is to assess lake water quality on approximately 8000 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, WDNR 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 WDNR-Science Services activity, performed annually, now has 25 years of record. At least two water clarity values from within a 3-year period in summer 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 & Training
     Data and Image processing
     SWIMS Data flow QA checks
     SWIMS Data Management Checks

Data Management

All database records and image files are archived at the Science Operations Center. A file containing the Secchi estimates is sent annually to the lakes program. Data are also stored in the SWIMS data base.


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 Integrated Water Quality Report to Congress (every two years). The next reporting period is 2016. The data will be used for key parameter package analyses and statewide condition summaries.

Programmatic Evaluation

This monitoring is funded, and hence evaluated, annually by the Lakes program. This effort has proved to be an extremely cost effective (12K annual) and efficient method to produce a sizable database for the agency as well as the public and scientific community. In addition, General Purpose Revenue is funding a project position from 2014-2016 that focuses on this work.

Last revised:

Tuesday May 30 2017