One of the most heartbreaking events in the ocean world is a dolphin stranding on a beach, alive but unable to return to the sea. It happens with surprising regularity worldwide, including in Hawaiian waters. The causes range from natural illness and injury to human-driven threats like sonar noise and ocean pollution. Here is a clear look at why it happens, what science has figured out, and what you should do if you ever encounter a stranded marine mammal on an Oahu beach.