Mapping Mercury in San Francisco Bay

By Western Geographic Science Center May 15, 2025

Scientists at the USGS are tracking mercury pollution in the Bay using remote sensing technology, creating detailed maps to monitor mercury pollution and support wetland restoration in a rapidly changing estuary.

Project page: Remote Sensing of Mercury Pollution in South San Francisco Bay

The Remote Sensing of Mercury Pollution in South San Francisco Bay project aims to create maps of multiple chemical forms—or “species”—of mercury across time and space, giving resource managers new tools to monitor water quality, especially after extreme storms. By combining satellite imagery, shipboard radiometry, and in-water sampling, researchers are building a time series of data on mercury species, including methylmercury, a particularly dangerous form that accumulates in fish and other wildlife.

A Legacy of Gold—and Contamination

Mercury pollution in the Bay Area has deep roots. During the California Gold Rush, mercury was used to extract gold from ore, and the runoff from those operations continues to contaminate waterways today. Mercury is also introduced through urban runoff and atmospheric deposition.

Methylmercury is a potent neurotoxin that affects top predators, birds, and even humans who consume fish from the bay. Understanding where and when mercury levels spike is crucial to ecosystem health.

This is especially important as climate-driven storms and floods become more frequent, churning up bottom sediments and releasing previously trapped mercury into the water column.

Read a news story about this project, "Tracking Quicksilver", published by the University of California, Santa Cruz.

Wetland Restoration Meets New Technology

At the same time, the Bay is the focus of some of the largest wetland restoration efforts in the country, led by groups like the South Bay Salt Pond Restoration Project. Their work to convert more than 15,000 acres of former salt ponds into healthy tidal wetlands is helping restore habitat and improve water quality—but it also changes how mercury moves through the system.

To help navigate this complex landscape, USGS scientists are turning to a multi-pronged data approach. Satellite-based remote sensing provides broad, repeatable coverage over time, while ship-based radiometers and in-water sensors provide high-resolution information on the physical properties of water. Together, these tools allow researchers to create dynamic maps that reveal how mercury concentrations shift after storms, between tides, and through seasons.