biologists working in Bangladesh have found a thriving population of 6,000 Irrawaddy dolphins, a species restricted to brackish bays and rivers from southern Asia to northern Australia that marine mammal experts had worried was vulnerable to extinction.

a long-term threat to the dolphins from global warming, which climate studies project will raise sea levels and change the river flows as Himalayan glaciers erode

Dolphin and porpoise species that have adapted to rivers and deltas around the world have long been considered some of the most vulnerable of marine mammals because of their restricted habitats. In 2007, experts concluded that the baiji, a river dolphin that thrived in the Yangtze River for 20 million years in what is today China, had been driven extinct

vaquita, a porpoise living in waters where the Colorado River empties into the Gulf of California, is critically endangered, biologists say, depleted by fishing nets and the disruptions in the river’s flow from dam construction