Concentrations of the pesticide Dieldrin in mussels along the northern shore of Monterey Bay have exceeded human health alert levels, posing a potential risk to both wildlife and humans. Pesticide concentrations in mussels have generally declined over time, although large increases occur following extreme rainfall events, providing a direct link between storm runoff, river discharges and effects on biological resources. The 2016 and 2017 CCLEAN annual reports identified several of these large increases following high runoff events.