Locomotion in an aquatic environment, termed aquatic locomotion, has two major forms: movement by swimming and movement by propulsion in contact with a substrate. Animals that are capable of swimming include various arthropods, fish, invertebrates, dolphins and whales among others. Freely-swimming animals are efficient swimmers for their ability to control water drag and for being able to manage their buoyancy. Invertebrates, such as mollusks, are able to propel themselves through water jets. Protozoans, such as ciliates, flagellates, and pseudopods have cilia, flagella, and pseudopod, respectively, for movement in a fluid or aqueous environment. Advanced swimmers, such as fish, are able to swim through the water through undulatory movements, i.e. creating undulations with their bodies to thrust them forward. Eel-shaped fish, for instance, undulate their entire body whereas streamlined fish, such as salmon, do so only at the caudal portion of their body. Based on body-caudal fin propulsion, there are different types of swimmers: the anguilliforms, the subcarangiform, the carangiform, the thunniform, and the ostraciform.
Bottom-dwelling aquatic animals, such as lobsters, are capable of walking at the substrate of seas or oceans.