The acceleration of the loading of nutrients to a lake by natural or human-induced causes. The increased rate of delivery of nutrients results in increased production of algae and consequently, poor water transparency. Human-induced (cultural) eutrophication may be caused by input of treated sewage to a lake, deforestation of a watershed, or the urbanization of a watershed.
A little insight on Lake Erie’s eutrophication problems: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3631662/
Glossary of stream, lake and watershed terms. (n.d.). Retrieved February 15, 2017, from http://kingcounty.gov/services/environment/watersheds/general-information/glossary.aspx