Unlike the amphibious seals, cetaceans (dolphins, whales, and porpoises) are completely out of their element once on land. When these animals come ashore it's almost always an indication of a serious health problem. To complicate matters, the very process of stranding can be catastrophic for a cetacean - even for one who has simply lost its way and becomes trapped by an outgoing tide. Once ashore, a cascade of physiological changes occurs, often resulting in shock and death. It's imperative that stranded cetaceans be given proper supportive care as soon as possible in order to mitigate this process.
The causes of strandings typically involve illness or injury, but there are exceptions. Strandings sometimes are simply the result of an animal being in the wrong place at the wrong time. Harbor porpoises, for example, can become trapped in a marsh during an outgoing tide. Heavy seas resulting from storms can leave animals exhausted, disoriented, or separated from their group. And regrettably, human interaction (by entanglement in fishing gear, ship strike, or gunshot) is sometimes the culprit.