Last week, Hoboken residents spotted something fishy while walking along the Hudson. A large scaly creature broke the surface of the river, sunning itself close to shore just long enough for interested locals to snap a shot. When the picture was reposted to Hoboken Girl’s Instagram, people jokingly guessed that the animal could be anything from a lost alligator to a river monster. After a more serious review, it was determined that the photo likely captured the endangered Atlantic Sturgeon. Here’s what we know about the species, and what this sighting might mean for the Hudson River ecosystem.