Mercury in Fish

Mercury in Sierra Nevada watersheds is a toxic remnant of the 19th century Gold Rush. Mined in the Coast Range and transported to the Sierra to improve gold recovery, mercury continues to wash off of mine sites and into water bodies where it can become bioavailable and enter the aquatic food web. Consumption of contaminated fish is the primary exposure pathway to mercury.

Mercury, a developmental neurotoxin, can cause irreversible cognitive impacts in infants and children. Exposure prevention is as simple as knowing which locally caught fish are safe to eat and which species should be avoided. The task at hand is ensuring clear and equitable communication of this important public health information.

Posting fish consumption advisories

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Californians who consume locally caught fish – from rural headwater communities to downstream cities in the Bay-Delta – are at risk for exposure to neurotoxic mercury. Widespread mercury contamination, in particular in the Coast Range where it was mined and in the Sierra Nevada where it was used, is a legacy of the 19th century Gold Rush. Millions of pounds of mercury were brought to the Sierra for use in gold processing, and approximately 10%-30% was lost to the environment and continues to wash off of mine sites during every major rain event.

Historic mining is the main source of mercury in California water bodies, and mercury is the driver behind 97% of California’s Office of Health Hazard Assessment (OEHHA) fish consumption advisories. The primary pathway of human exposure to mercury is the consumption of contaminated fish. Exposure to even low levels of mercury is linked to adverse outcomes that can include damage to the brain, nervous system, kidneys, immune system, and cardiovascular health, especially for vulnerable populations like developmentally sensitive children and women of childbearing age, Tribes for whom wild-caught fish is a cultural lifeway, and subsistence anglers.

The majority of water bodies in the headwater region that The Sierra Fund serves are listed as mercury-impaired under Section 303(d) of the Clean Water Act and black bass species are frequently listed in site-specific OEHHA fish advisories as “Do Not Eat” for women of child-bearing age and children. Furthermore, mercury from legacy mines contributes 96% of the ongoing mercury contamination to the San Francisco Bay and Delta and is thus the driver behind mercury in fish downstream.

The Sierra Fund’s Vision for empowering Sierra Nevada communities to protect their health from mercury in fish

The Sierra Fund’s vision for its work around mercury in fish is to increase equitable access to information about how to safely consume locally caught fish in California so that all populations can enjoy the full beneficial use value of public water bodies. The Sierra Fund supports implementation of legislation signed into law in 2020 (AB 762) that requires posting of site-specific fish advisories as an opportunity to increase awareness about how dangerous eating locally caught mercury-contaminated fish in California can be, particularly in the twenty-two mining-impacted counties that make up the Sierra Nevada region as well as the populations directly downstream. The Sierra Fund’s work highlights the need for equitable messaging that communicates safe eating guidelines in a multitude of languages for diverse species of fish consumed across a broad range of ethnic groups. The Sierra Fund also advocates for consistent messaging and, to this end, urges that water bodies known to have high levels of mercury are prioritized for data collection so that site-specific advisories can be developed and posted under AB 762. Finally, The Sierra Fund urges that statewide advisories be posted at applicable water bodies without site-specific advice.

Mercury Pilot Projects

The Sierra Fund has worked on the topic of mercury in fish for over a decade. The Sierra Fund’s efforts today build upon the successes of three pilot projects described below.

Gold Country Angler Survey

To understand mercury exposure potential and effectiveness of posting fish advisories as a strategy to improve health outcomes The Sierra Fund surveyed over 400 anglers between 2009-2016. As a result of this survey The Sierra Fund has been able to inform data collection efforts that support the development of healthy eating guidelines for species of fish that are actually being caught and consumed by diverse angling populations in the Sierra region.

Post It Day

Through annual volunteer Post It Day event The Sierra Fund has posted 140 state-issued fish consumption advisories in 118 locations at 20 water bodies, 9 of which are posted in Spanish and English. As a result of this project, The Sierra Fund incentivized both the largest landowner (Tahoe National Forest) and the largest water body manager (Nevada Irrigation District) in the Sierra region to post fish consumption advisories annually at water bodies under their purview.

Sierra Fish Tissue Study

The Sierra Fund collected and submitted for laboratory analysis over 200 fish samples from the Sierra region to provide OEHHA with data for use in the development of site-specific fish advisories. As a result of ongoing coordination with OEHHA three new fish advisories for the Sierra region were released in 2018 and one new advisory was issued in 2020.