The Los Angeles area of the Southern California Bight is the focal point of this field-oriented ECOHAB research program to investigate the relationship between freshwater inputs from a highly urbanized coastal region and blooms of the toxic diatom Pseudo-nitzschia. The Los Angeles Harbor and adjacent coastal ocean are periodically influenced by runoff from 3 major rivers. Freshwater discharge from the Los Angeles River, San Gabriel River and Santa Ana River contribute substantial amounts of inorganic nutrients, labile organic compounds and trace metals to the coastal region. River input is strongly episodic, highly channelized, and restricted primarily to winter/early spring. It is hypothesized that these meteorological events greatly influence phytoplankton dynamics and the formation of harmful algal blooms. This research program examines the connection between storm events and Pseudo-nitzschia species success and the production of domoic acid (DA) in coastal communities.