On August 27, the world marks World Lake Day for the first time since it was added to the UN calendar in 2025. For the One Heritage campaign, it’s a chance to point out something easy to miss: lakes and lagoons aren’t only about water. They’re also home to some of the rarest dolphins on Earth.

Mention dolphins, and most people picture the open ocean. But a handful of species spend their entire lives in fresh or brackish water — in the rivers of Asia and South America, and sometimes in lakes and lagoons.

Chilika Lake, in India’s Odisha state, is Asia’s largest lagoon and the world’s second-largest. It’s home to the largest single lagoon population of Irrawaddy dolphins (Orcaella brevirostris) anywhere on Earth — around 150 individuals in recent counts. The species as a whole is classified as Endangered by the IUCN, while its riverine subpopulations in the Mekong, Ayeyarwady, and Mahakam river systems are Critically Endangered.

Two more species in South Asia never reach the ocean at all: the Ganges river dolphin (Platanista gangetica) and its close relative, the Indus river dolphin (Platanista minor), found mainly in Pakistan. A small isolated population of Indus river dolphins in India’s Beas River has been cut off from the main range by irrigation barrages — a 2024 survey counted only about three individuals left there.

In South America, the Amazon river dolphin, or boto (Inia geoffrensis), lives in the Amazon and Orinoco basins — a pink freshwater dolphin still considered the healthiest of the river dolphin species, though it too is classified as Endangered. A very different fate met the baiji, China’s Yangtze River dolphin: declared extinct in 2006, it became the first cetacean species in modern history driven to extinction by human activity.