LAKE POWELL — Scientists are just beginning to analyze data collected earlier this year during an unusual expedition on Lake Powell.
They're trying to assess why toxic mercury is a problem for fish — and humans who eat them.
Two research vessels traveled up and down Lake Powell earlier this year, one taking samples of water, the other probing sediments at the bottom of the lake.
“They’re beginning to analyze this, and some data is rolling in,” said Mark Anderson, aquatic ecologist with the National Park Service.
Anderson said toxic mercury is a problem for lakes across the country. It builds up in the tissues of fish, potentially harming people who eat too many of them.
“It causes real neurological problems,” Anderson said. “In developing children in particular.”
Two years ago, officials declared a fish-consumption advisory at Lake Powell. It applied only to striped bass in the lower half of the lake where toxic mercury is above national averages.
“Statistically, we can show that it’s higher here. But it’s a relatively small amount. Individual fish can be very high,” Anderson said.
One mystery is why the concentration of toxic mercury is worse at the lower end of the lake. It’s caused some people to wonder if there’s a localized source of pollution.
The working theory is that the real culprit is a bit of bio-chemistry in the lake. Mercury is toxic only if it becomes methylized, a process assisted by algae and bacteria. The lower end of the lake has clearer water than the silty upper end, so there's more algae.
“More algae being borne, more algae dying, more algae decomposing, more methylization of mercury. That would be the hypothesis,” Anderson said.
If the studies firm up the theory, it would likely point the finger much further away to power plants in China delivering mercury to lakes across the U.S. It’s possible that conditions in lower Lake Powell just make it more toxic.