The U.S. Geological Survey says it's still unclear how much lasting damage the mercury is causing. That will be the focus of another study expected to be completed early next year.

The new study says the amount of mercury found in eared grebes increases during periods when they dine heavily on the lake's brine shrimp.

Nathan Darnall, an ecologist with U.S. Fish and Wildlife Service, says mercury can cause neurological problems for birds and affect their ability to fight off diseases. He says there's no evidence that's happening at the lake.

Meanwhile, the debate continues about where the elevated levels of mercury at the Great Salt Lake are coming from.

Mercury occurs naturally but also comes from industrial emissions and other human-caused sources. Dave Naftz, the main author of the USGS report, said mercury is in the atmosphere and comes from sources around the world.

''We have global sources of mercury coming into the atmosphere from China,'' Naftz noted. He also acknowledged regional sources such as industrial activity in Nevada.

Last month, the Utah Department of Environmental Quality issued methods for identifying sources of mercury in lakes and rivers throughout the state.

Aside from warnings about eating fish from waters with elevated mercury levels, the USGS has warned against eating three types of waterfowl living around the lake.

Jeff Salt, director of Great Salt Lakekeeper, wants state officials to get more involved in dealing with mercury in Utah.

''Our governor and state Legislature really need to step up and recognize the potential risks that mercury compounds can have on our human and wildlife populations and allocate significantly more funds for critical research and monitoring needs,'' Salt said.