The freshwater Irrawaddy dolphin, known as pla ka in Lao, is one of the world's most endangered species; according to a 2008 study, less than 50 now remain in the Mekong. The Irrawaddy has mythical origins. According to Lao and Khmer legend, a beautiful maiden, in despair over being forced to marry a snake, attempted suicide by jumping into the Mekong. But the gods intervened, saving her life by transforming her into a dolphin.

Lao people do not traditionally hunt the dolphins, but the Irrawaddy have been casualties of over-fishing, getting tangled in nets. New dams in the Mekong have altered their ecosystem, further threatening their survival.

Catching a glimpse of these majestic animals—which look more like orcas than dolphins—can be a thrilling experience. The least obtrusive way to visit the Irrawaddy is in a kayak or other non-motorized boat. If you go by motorboat and do spot dolphins, ask your driver to cut the engine when you're still 100 yards or so away. You can then paddle closer to the animals without disturbing them. Do not try to swim with the dolphins, and—of course—don't throw any trash into the water.