When I plunge into San Francisco Bay in spring, I’m swimming through a cool green fish stew. This is the season when microscopic diatoms are proliferating. Masses of these  jewel-like, silica-walled plankton are turning sunlight into sugar, providing the base for an incredible production of life. The diatoms feed the animal plankton that feed the infant shrimp that feed the juvenile California halibut and Pacific herring. The strands of eelgrass lengthen with the days and shelter them all.

Unlike the hikers on land who enjoy vistas of poppies in bloom, we swimmers can’t see the explosion of vernal life all around us. The ingredients in this soup are hidden from the human eye by the very density of organic activity: The water is cloudy with the plankton and sediment that make the estuary so hospitable to baby fish and other animals. 

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Susan Kuramoto Moffat has written for the Los Angeles Times, The Wall Street Journal, the Associated Press, and Estuary News from places including Tokyo, Seoul, Southern California, and San Francisco Bay Area. She is working on a book about urban wilds.