Most of the world's mammals need water only for drinking. However, some mammals species live all their lives in or on the water. All aquatic mammals descend from land-dwelling animals that have migrated back to water. Because of this, every aquatic mammal has a lung and needs to breathe on the surface of the water.


Beavers are rodents.

Whales have linear bodies that resemble those of sharks and other fish. They are the mammals most fully adapted to aquatic life. Whales give birth and raise their young in the water. The only species of whale found in the Baltic Sea is the endangered harbour porpoise. 

Seals are likewise well adapted to aquatic life. Their body shape is ideal for diving and moving in the water, which probvides the seals an advantage when fishing. They only visit the land or the ice to rest and to give birth.

Minks and otters are predators that like to live near the water. Both of these species are mustelids.

Beavers and muskrats are rodents that like to live near lakes and rivers. Dam-building beavers are second only to humans when considering how much the species' actions modify Finnish water environments. Muskrats are rodents that have been brought to Finland from North America.