Scientists Consider Posting Mercury Warnings at 2 Sierra Rivers

East of here, streams and rivers spill from the Sierra Nevada with an angler’s bounty of trout and catfish, bluegill and bass.

But the fishing could soon come with a warning.

For the first time, government scientists are investigating whether health advisories are warranted for a pair of pristine Sierra waterways tainted by mercury during the Gold Rush.

Although final results aren’t in, some local officials predict that the U.S. Geological Survey study of the Bear and South Yuba rivers might push the state to post warnings about eating fish that accumulate the toxic metal.

A remnant of the go-go days of the ‘49ers, mercury was used to separate gold from raw ore. Much of it slopped out of sluice boxes and into streams, where it persists to this day.

In water, mercury is absorbed by microscopic bacteria and transformed into an organic form known as methyl mercury. It then hops up the aquatic food chain from tiny invertebrates to small fish, and finally concentrates in the biggest fish, such as bass.

Preliminary findings indicate that mercury levels in some Sierra fish exceed the U.S. Food and Drug Administration’s limit of 1 part per million for commercial seafood, local officials say.

A formal listing is at least a year away, but officials in several Sierra counties are nervous about the potential economic impact. The rural region, once a haven of timber and mining, now depends on outdoor recreation and tourism.

But some officials are confident that an aggressive attack on the problem and a public education campaign can ease concerns about mercury, which is typically a health concern only for small children and women of childbearing age.

“I’m erring on the side of caution,” said Nevada County Supervisor Elizabeth Martin. “I’d like to see this as an early warning. And I’d like to see us break the characteristic response of rural counties--denial and avoidance.”

Officials at the state agency that makes the final call on fish advisories say it is too early to tell if enough good data are available to properly assess the risk.

“We try to keep focused on the science,” said Allan Hirsch, spokesman for the state Office of Environmental Health Hazard Assessment. “You don’t want to overreact. On the other hand, you want to understand what, if anything, is in the fish.”

Nationwide, mercury pollution has prompted fish advisories at more than 1,900 lakes and estuaries, triple the number for all other pollutants combined.

California currently has fish advisories at 13 bodies of water, including the San Francisco Bay and delta, the final resting place for much of the mercury that flowed out of Mother Lode mines. The other posted sites are lakes and streams in the Coastal Range, where a rich belt of mercury was mined and shipped to prospectors in the Sierra beginning 150 years ago.

The health risks of mercury poisoning are well documented, ranging from tingling in the extremities to death. In Japan, a mercury outbreak in polluted Minimata Bay killed hundreds of people in the 1950s and 1960s.

But the levels of mercury in California are far lower, and scientists remain divided over what neurological effects might be caused.

Concerns remain that exposure to even relatively small amounts of mercury from tainted fish can pose problems for children younger than 6 and those in the womb. Some scientists believe that walking or other skills may be delayed.

Hirsch said the formal assessment process will take about a year. If a state advisory is issued, the warning will be included in Fish and Game guidebooks provided when anglers get a fishing license. Typically, the advisories specify the number of meals of fish allowable without any adverse health risk.

Amid the region’s array of scenic lakes and mountainside fishing spots, there’s more than a little fear. But it’s about tourists being turned away, not endangered health.

“Of course I’m worried,” said Dave Munro, owner of Skipper’s Cove Marina at Englebright Lake, which is fed by the South Yuba.

He noted that the prime catch in Englebright, as in much of the watershed fed by the Bear and Yuba rivers, is rainbow trout, a species low on the food chain that rarely accumulates much mercury. But the lake also has bass, meaning that the site could be pulled into any posting.

Nevada County Supervisor Martin acknowledged the concern.

“I absolutely worry about the effect on tourism,” she said. But she noted that many people “have grown so used to toxic warnings” that a posted fish advisory “doesn’t have the same slap in the face it would have 20 years ago.”

Cleaning up the mess could prove difficult and costly. The U.S. Environmental Protection Agency is spending up to $1.2 million just to clean up one abandoned mine tunnel near Dutch Flat.

Officials also hope to draw in the private sector--the modern-day gold miners. A plan is afoot to collect mercury the miners gather as they comb Sierra streams with suction dredges.

Martin, meanwhile, talks of installing permanent mercury traps in spots where the stuff spews from mines and into streams. “We want to leap ahead of this,” she said.