Blackwater rivers, like the Ogeechee and Canoochee and other southeast Georgia streams, have a unique water chemistry that converts mercury entering the river into it's most toxic form, methylmercury.

Additionally a prevalence of large areas of adjacent wetlands also speed up this conversion. 

In fact, recent research from the US Geological Survey found that rural streams are more contaminated with mercury than urban streams due to the prevalance of a lot of wetlands.  While these areas are really important to filtering out most pollutants, when mercury enters the rivers from air pollution from coal-fired power plants, these wetland areas hold and convert the mercury and allow it to enter the food web.

From Environmental Science and Technology, 2009:  "To control mercury levels in fish, ideally there must be a way to control mercury emissions coming from coal-fired power plants, smelters, and other sources, Driscoll says. Yet several mitigating factors are also at work, as shown by the differences the USGS team found in urban versus nonurban streams. Most people would expect more mercury in fish in urban streams, but the new research indicates that that’s not the case. For example, in urban streams, mercury isn’t available to biota because of the relatively high sulfur and sulfate levels, which seem to bind up the available mercury, as indicated in the paper by Mark Marvin-DiPasquale et al."

Last updated on March 5, 2010 by Ogeechee Riverkeeper