Into this seasonal sea, which remains for half the year, swims the Amazon river dolphin, or boto. Botos have the characteristic dolphin smile and, unlike their marine cousins, bulbous foreheads ...

There’s the South Asian river dolphin (Platanista genus) and the Amazon river dolphin (Inia genus), also known as the pink river dolphin, and the two groups include several species and subspecies.

But the Amazon river dolphin — endangered animals known for their unusual color — had always stood out as one of the river’s most resilient species. Now at least 125 were dead.

High mercury levels have been noted in the dolphins of Florida’s Everglades and the dolphin-hunting town of Taiji, Japan. The Orinoco River, which divides Venezuela and Colombia in the Amazon ...