This project seeks to characterize copper toxicity in the San Francisco Bay-Delta by analyzing total dissolved copper and copper-binding organic ligand concentrations. Preliminary findings suggest that dissolved copper is strongly complexed by organic ligands in all samples collected. In North San Francisco Bay-Delta, these ligands reduce current bioavailable copper (Cu2+) concentrations to levels that are likely harmless to local aquatic microorganisms. Preliminary field sampling also suggests that Suisun Slough is a much larger source of copperbinding ligands to North San Francisco Bay, on a per-volume basis, than either the San Joaquin or Sacramento rivers. Among the objectives of the project’s final year: to assess the photolability of copper-binding ligands and analyze samples for dissolved iron speciation. Iron speciation has never been documented for San Francisco Bay, and may provide additional insight into trace metal cycling in these waters.