From the EPA's Fish Advisory Newsletter:
Group tackles mercury woes. Cortez, CO -- Earlier this year, a mercury advisory was issued for the Vallecito Reservoir. It warned people about consuming walleye and northern pike from the lake. The source of the mercury has not been pinpointed and it may not be a single factor. Even so, a group of community members, tribes, interest groups, industry and government representatives have formed the Four Corners Air Quality Task Force. The group plans on working on all air quality issues including mercury emissions from coal-fired power plants. They are also hoping to track down the cause of the mercury contamination in the Vallecito Reservoir.
Source: The Durango Herald - August 10, 2006
Hint: It is the power plants.