During a NOAA Ship Okeanos Explorer 2018 expedition to the Gulf of Mexico, remotely operated vehicle Deep Discoverer (D2) crested a low rise on the seafloor and peered into a sediment-lined depression filled with fluid, which was a brine pool. Panning up from the pool, D2 imaged long, blue-gray-black streaks of stained sediment on the otherwise tan-colored slope seen in this photo—the team had found a brine waterfall! From: A Waterfall Under the Sea.