On a weekday morning, Johnnie Heal caught four largemouth bass from a pier in Clearlake Oaks, but tossed three back in the water.
“I don’t eat anything out of this lake,” said Heal, 32, who likes fishing for sport. “They say you can eat so many a month. But if you have to put a limit on it, I’m not going eat it.”
But the fourth bass he gave to an elderly woman who wanted it for her meal.
Because of high mercury levels in Clear Lake fish, women older than 45 and all men should eat only one serving per week of largemouth bass, according to guidelines issued by California’s Office of Environmental Assessment.
Warnings and guidelines, which are posted at public boat ramps, are less restrictive for other species such as carp, crappie, bluegill and catfish, allowing for several servings per week.
But women of child-bearing age and children are advised not to eat any largemouth bass at all out of Clear Lake and to limit consumption of other fish to only one serving per week.
There are similar warnings for many of the state’s other lakes and streams.
In a 2007 survey of more than 200 of the most popular fishing lakes in California, more than 50 had at least one fish species with high enough methylmercury consumptions to recommend no consumption for children younger than 18, or for women of child-bearing age, according to the California Water Resources Control Board.
“The mercury problem is widespread,” said Janis Cooke, a senior environmental scientist with the state’s Central Valley Regional Water Quality Control Board. “There are many reservoirs across the state where the concentrations in the large fish people like to take home and eat are equally as bad as Clear Lake.”
The poor and Native Americans who traditionally have fished at Clear Lake are most impacted. For some, the lake’s fish are a diet staple.
Lake County has a high unemployment rate and median household income of $36,400, about 60 percent of the state’s $61,900 median.
“The reality is, people are eating fish to survive,” said Sarah Ryan, environmental director for the approximate 1,000-member Big Valley Rancheria near Lakeport. “There are a lot of people eating large amounts of fish from this lake.”
Big Valley Rancheria, in conjunction with state Fish and Wildlife researchers, took fish tissue samples around the lake over a period of several months in 2015, marking more than 40 years the problem has been documented.
Of the 20 fish taken, 14 had mercury levels above the maximum pollution limit. In some cases, largemouth bass had more than five times the acceptable level.
Dr. Karen Tait, Lake County’s health officer, shares concerns that Lake County residents are exposing themselves to unsafe levels of methylmercury. She said they need to follow safe fish consumption guidelines because mercury toxicity symptoms aren’t always obvious.
“Since the effects may not be immediately apparent (and generally aren’t), prevention of adverse health effects really depends on an informed public,” she wrote in an email.
Old abandoned mines, like Sulphur Bank on Clear Lake’s southeastern end, are a prime source of mercury contamination in California. But mercury also comes from natural sources and fallout from burning coal and other fuels.