Editing Great Salt Lake (section)

===Elevated mercury levels===
{{missing information|section|significant reduction in methylmercury after 2013 culvert cut and drought ([https://unews.utah.edu/gsl-mercury/ utah.edu 2017])|date=May 2022}}
During a survey in the mid-1990s, [[U.S. Geological Survey]] and [[U.S. Fish and Wildlife Service]] researchers discovered a high level of [[methylmercury]] in the Great Salt Lake with 25 [[nanogram]]s per [[liter]] of water. For comparison, a fish consumption advisory was issued at the [[Florida Everglades]] after water there was found to contain 1 nanogram per liter.<ref name="Trib mercury">{{cite news |url = http://www.sltrib.com/utah/ci_2577720 |title = Toxic mercury lurking in Great Salt Lake | publisher = Salt Lake Tribune |access-date = November 29, 2007 |archive-url = https://web.archive.org/web/20071223041317/http://www.sltrib.com/utah/ci_2577720 |archive-date = December 23, 2007 |url-status = dead |df = mdy-all }}</ref> The extremely high methylmercury concentrations have been only in the lake's anoxic deep brine layer ([[monimolimnion]]) below a depth of {{convert|20|ft|m}}, but concentrations are also moderately high up in the water column where there is oxygen to support brine shrimp and brine flies.

The toxic metal shows up throughout the lake's food chain, from brine shrimp to eared grebes and cinnamon teal.

The finding of high mercury levels prompted further studies,<ref>{{cite web |url = http://health.utah.gov/epi/enviroepi/activities/HotTopics/HotTopics/Waterfowl%20Advisory/UtahWaterfowlAdvisory0506.html |title = Utah Waterfowl Advisory |publisher = Utah Office of Epidemiology |access-date = August 25, 2006 |archive-date = September 24, 2006 |archive-url = https://web.archive.org/web/20060924081813/http://health.utah.gov/epi/enviroepi/activities/HotTopics/HotTopics/Waterfowl%20Advisory/UtahWaterfowlAdvisory0506.html |url-status = live }}</ref> and a health advisory warning hunters not to eat [[common goldeneye]] or [[northern shoveler]], two species of [[duck]] found in the lake. It has been stated that this does not pose a risk to other recreational users of the lake.<ref>{{cite press release |url = http://www.wildlife.utah.gov/news/05-09/mercury_duck.php |title = High mercury levels found in two duck species |publisher = Utah Division of Wildlife Resources |access-date = August 25, 2006 |archive-date = February 1, 2010 |archive-url = https://web.archive.org/web/20100201202949/http://wildlife.utah.gov/news/05-09/mercury_duck.php |url-status = live }}</ref>

After later studies were conducted with a larger number of birds, the advisories were revised and another was added for [[cinnamon teal]]. Seven other species of duck were studied and found to have levels of mercury below EPA guidelines, thus being determined safe to eat.<ref>{{cite press release |url = http://wildlife.utah.gov/news/06-09/mercury.php |title = Duck mercury advisories revised |publisher = Utah Division of Wildlife Resources |access-date = September 21, 2006 |archive-date = January 7, 2010 |archive-url = https://web.archive.org/web/20100107095729/http://wildlife.utah.gov/news/06-09/mercury.php |url-status = live }}</ref>

A study in 2010 suggested that the main source of the mercury is from atmospheric deposition from worldwide industry, rather than local sources. As water levels rise and fall, mercury accumulation does as well. About 16% of the mercury is from rivers, and 84% is from the atmosphere as an inorganic form, which is converted into more toxic methylmercury by bacteria which thrive in the more saline water of the North arm affected by the causeway.<ref name="Global mercury"/>  A 2020 study found high concentrations of mercury in the lake's sediments, a consequence from smelting and mining activities in the surrounding mountains.<ref>Wurtsbaugh et al. 2020.  Effects of a century of mining and industrial production on metal contamination of a model saline ecosystem, Great Salt Lake, Utah. Environmental Pollution 266: 115072.  doi.org/10.1016/j.envpol.2020.115072</ref> The mercury and other metals can contaminate the overlying water, and in turn, move into brine shrimp and other organisms.<ref>Jones & Wurtsbaugh. 2014. The Great Salt Lake's monimolimnion and its importance for mercury bioaccumulation in brine shrimp (Artemia franciscana).  Limnol. Oceanography 59 (1): 141-155.   https://doi.org/10.4319/lo.2014.59.1.0141</ref>