Limnology classifies lakes (or other bodies of water) according to the trophic state index. An oligotrophic lake is characterised by relatively low levels of primary production and low levels of nutrients. A eutrophic lake has high levels of primary productivity due to very high nutrient levels. Eutrophication of a lake can lead to algal blooms. Dystrophic lakes have high levels of humic matter and typically has yellow-brown, tea-coloured waters. These categories do not have rigid specifications; the classification system can be seen as more of a spectrum encompassing the various levels of aquatic productivity.
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The History of Limnology at the University of Wisconsin–Madison: A digital resource documenting three generations of limnological research in Wisconsin. Much of the collection comes from the archives of the UW–Madison Center for Limnology. It focuses on three important pioneers of limnology, Dr. Edward A. Birge, Chancey Juday and Arthur D. Hasler, as well as Wisconsin research laboratories and field equipment. Presented by the University of Wisconsin Digital Collections Center.