The Sausalito Hum — When Fish Made an Entire City Vibrate (2014)

In 2014, residents of Sausalito, California — a bayside community across the Golden Gate from San Francisco — began reporting a loud humming that shook their houseboats and waterfront homes, primarily during summer and fall nights. Complaints to city officials increased, and an investigation was launched. The source turned out to be one of the more remarkable discoveries in Hum research: the plainfin midshipman fish (Porichthys notatus), a species that produces an extraordinarily loud, low-frequency mating call by vibrating its swim bladder. During mating season, male midshipman fish gather in dense colonies on the bay floor beneath Sausalito's houseboat communities and produce a continuous, droning hum that can exceed 100 decibels at close range — loud enough to vibrate the hulls of houseboats and be heard clearly inside homes. The Sausalito Hum is significant because it represents one of the few cases where a mysterious Hum was definitively traced to its source, and that source turned out to be biological rather than industrial or geological. It serves as a reminder that some Hum cases may have natural explanations that are simply very difficult to anticipate.