Data collected by Birge, Juday, and collaborators, mostly in north-central Wisconsin, from 1900 through 1943; generally one sampling event per lake during the summer, but on some lakes, especially around Trout Lake Station, several sampling events for several successive years. This data set contains both surface data (depth of zero) and multi-depth data. Note that not all variables were measured on all lakes. Documentation: Johnson, M.D. (1984) Documentation and quality assurance of the computer files of historical water chemistry data from the Wisconsin Northern Highland Lake District (the Birge and Juday data).Wisconsin DNR Technical Report. Note: Values of -99999 in water quality data indicate trace amount of parameter was present. Number of sites: 663 (generally one sampling point per lake; occasionally, several sampling points per lake on multibasin, large lakes).<u> Note:</u> This data set was updated in 2013 to include multi-depth and additional surface data for a large subset of lakes. These additions expanded the number of sites from 605 to 663, and expanded the date range from 1925-1942 to 1900-1943 . Furthermore, 14 lakes in Minnesota were added to the data set contributing additional surface and multi-depth data. Another dataset was added in 2013 collected by Wisconsin limnologists Chauncey Juday and Edward Birge, this data set contains variables that are still commonly used in research. For example, temperature, dissolved carbon dioxide, color, pH, secchi disk, plankton, and silica. However, the data set also includes variables that are not commonly used, for example, crude protein, non-amino nitrogen, ether extract, and total organic and inorganic material. These data are characteristic of water chemistry analysis from the time in which they were compiled (5/31/1915 - 8/29/1938). The data set features data from 586 different lakes, primarily lakes in the Northern Highland Lakes District of Wisconsin. However, there is also data from lakes in southeastern and southcentral Wisconsin. Furthermore, there is a minimal amount of data from lakes in Minnesota, Ohio,New York, Alaska, the Philippines, and the United Kingdom. Documentation:Birge, E.A., and Juday, C. 1922. The inland lakes of Wisconsin. The Plankton I. Its quantity and chemical composition. Bulletin, Wis. Geol. and Nat. Hist. Survey No. 64: (Scientific series 13), ix-222.