In spring 2021, an unexpected outbreak of sea mucus spread across the Marmara Sea in western Turkey as a foamy membrane on the water's surface. To help respond, we mapped its full extent using multi-band satellite imagery and automated classification, and published web maps that were updated every three days. Social media photographs and videos added a local, day-to-day view alongside the remote sensing. The complex water flow in the Marmara Sea makes it hard to train classification models, so we used an ongoing review process to keep the results accurate. The Metropolitan Municipality of Istanbul published the maps. The mucus cleared as temperatures at the end of the year, but it's expected to return.