During the global COVID‑19 lockdowns, we set out to quantify how human activity affected the underwater soundscape. Using open hydrophone networks, we ingested continuous acoustic streams and converted them into spectrograms, then applied analytics to track low‑frequency noise associated with shipping and coastal activity. The results, presented as an interactive web app at MonitorMyOcean.com, revealed pronounced regional and temporal drops in ambient ocean noise—evidence that human activity patterns measurably affect the marine acoustic environment.