Why do whales beach themselves?

Whale strandings, where whales swim onto shore and become stuck, can have many causes and often remain a mystery. A single stranded whale is frequently sick, injured, or old, and too weak to stay afloat in deep water. Mass strandings of highly social species, such as pilot whales, may happen when the group follows a sick or disoriented leader, since their strong social bonds keep them together even into danger. Gently sloping or complex coastlines can confuse the echolocation whales use to navigate, and loud underwater noise from storms or human activity may also disorient them. Rescuers sometimes refloat stranded whales, but success depends on how long they have been out of the water and their overall health.