This is a list of tetrapods that spend part of their life cycle or a significant fraction of their time in water.
Semiaquatic Tetrapoda are those that are primarily or partly terrestrial but that spend a large amount of time swimming or otherwise occupied in water, either as part of their life cycle or as an essential behavior (e.g. feeding). Some marine mammals, such the marine otter, the polar bear and pinnipeds, are semiaquatic, while others, such as the sea otter, cetaceans and sirenians, are fully aquatic. The only fully aquatic nonmarine mammals are several manatees (the Amazonian manatee and some populations of African manatee) and certain small cetaceans (river dolphins, the tucuxi, and some populations of Irrawaddy dolphin and finless porpoise). Among marine reptiles, marine iguanas and partly marine crocodiles (such as the saltwater crocodile and the American crocodile) are all semiaquatic. Sea turtles are almost fully aquatic, but must come ashore to lay eggs. Most sea snakes are ovoviviparous and fully aquatic (the exception being the oviparous, semiaquatic sea kraits). On the other hand, no bird species is fully aquatic, as all must lay and incubate their eggs, as well as begin raising their young, on land or ice. Most amphibians have an aquatic larval stage and are at least semiaquatic for that reason, but there are many exceptions to this generalization.
Monotremes
Platypus - (Ornithorhynchus anatinus)
Marsupials
Lutrine opossum - (Lutreolina crassicaudata)
Water opossum or yapok - (Chironectes minimus)
Tenrecs
Otter shrews
Web-footed tenrec
Primates
Allen's swamp monkey
Proboscis monkey
Rodents
Castorimorpha - beavers, pocket gophers, and kangaroo rats
Beavers
Caviomorpha - New World hystricognaths
Capybaras
Coypu
Paca
Myomorpha - mouse-like rodents
'Crab-eating rats'
European water vole
'Fish-eating rats'
'Marsh rats'
Muskrat
'Swamp rats'
'Water mice'
'Water rats'
Lagomorphs
Marsh rabbit
Swamp rabbit
Soricomorphs
Desmans
'Water shrews'
Carnivorans
Mustelidae - weasels and otters
Minks
Otters (except the sea otter)
Pinnipeds
Procyonidae - raccoons
Crab-eating raccoon - (Procyon cancrivorus)
Ursidae - bears
Polar bear - (Ursus maritimus)
Felidae - cats
Fishing cat
Flat-headed cat
Herpestidae - mongooses
Crab-eating mongoose
Viverridae - civets and genets
Aquatic genet
Perissodactyla
Rhinocerotidae - rhinos
Indian rhinoceros
Javan rhinoceros
Sumatran rhinoceros
Tapiridae - tapirs
Baird's tapir
Brazilian tapir
Malayan tapir
Artiodactyls
Bovidae - ruminants
Anoa
Sitatunga
Waterbuck
Wild water buffalo
Cervidae - deer
Chinese water deer
Marsh deer
Moose
Hippopotamidae - hippos
Hippopotamus
Pygmy hippopotamus
Tragulidae - mouse-deerGreater mouse-deer
Water chevrotain
Yellow-striped chevrotain
Austrodyptornithes
Penguin
Ducks
Geese
Swans
Herons
Kingfishers
Gulls
Pelicans
Sandpipers
Plovers
Auks
Jaegers
Dippers
Crocodilians
Lizards
Asian water monitor
Basiliscus (basilisks)
Dracaena (caiman lizards)
Galápagos marine iguana
Mertens' water monitor
Mitchell's water monitor
Nile monitor
Snakes
Anacondas
Cottonmouth
Crayfish snakes
Garter snakes
Mud snake
Rainbow snake
Sea kraits
Water cobras
'Water snakes'
Grass snake
Most turtles, excluding fully terrestrial box turtles, tortoises, and some Asian box turtles
Most amphibians have an aquatic larval stage and thus are at least semiaquatic by virtue of this fact. Many adult amphibians are also semiquatic (while others are fully aquatic or terrestrial). However, some amphibians lack an aquatic larval stage. Some frogs, such as most leiopelmatids, most ranixalids, some leptodactylids, some myobatrachids, Darwin's frog and the Seychelles frog, have nonaquatic tadpoles. Some caecilians, many frogs such as saddleback toads, most sooglossids and the greenhouse frog, and most plethodontid salamanders lay eggs on land in which the larvae develop into adult form before they hatch. The alpine salamander and African live-bearing toads (Nectophrynoides and Nimbaphrynoides) are ovoviviparous and give birth on land. Additionally, about 75% of caecilians are viviparous.
Most anurans (frogs and toads), but not the fully aquatic pipids, or fully aquatic members of other families such as Telmatobiidae
Some caecilians, such as ichthyophiids, rhinatrematids, Chthonerpeton and Nectocaecilia, but not including other fully aquatic typhlonectids
Most non-plethodontid salamanders, but not including the fully aquatic amphiumids, cryptobranchids, proteids, sirenids and various neotenic species in other families, such as Ambystoma mexicanum