Oarfish are the world’s largest bony fish, and they usually don’t come in to the beach. They like depths of around 650 feet, and as far down as 3,000 feet. But in March, a group affiliated with Chicago’s Shedd Aquarium encountered two beautiful oarfish swimming near the shore of the Sea of Cortés, in Mexico.

These silvery ribbons of fish can grow to enormous sizes—the two in the video are about 15 feet long, but oarfish can grow to be well over three times that size.

When oarfish end up in such shallow water it usually portends a bad end for the fish, as they don’t generally venture into that portion of the ocean unless they are injured or dying. Dissections of two oarfish that washed ashore last fall showed that one was severely infested with parasites. The other may just have been lost. From LiveScience:

Scientists with the U.S. National Oceanic and Atmospheric Administration's Southwest Fisheries Science Center performed a necropsy (an animal version of an autopsy) on the smaller oarfish that washed up north of San Diego. Russ Vetter, a NOAA biologist, said in a podcast from the agency that the fish was quite fresh and seems to have stranded shortly before it died....Vetter suspects the creatures may have been carried closer to shore by a strong ocean current, which the oarfish, being poor swimmers, could not escape.

Because of the rarity of sightings and the fishes' unforgettable shape, oarfish have entered the realm of legend: just look at the video footage, and you can easily imagine where tales of sea serpents might have started.