People of the Ocean

The People of the Ocean are a humanoid species that appeared in the series Ocean Girl (a.k.a. Ocean Odyssey).

Biology
The species is physically indistinguishable from humans, but internally they are quite different.

While they are capable of surviving on land, individuals must periodically enter a body of water to rehydrate their cells. If they fail to do this, they will dehydrate and die. They are capable of spending prolonged time beneath the ocean without breathing equipment, due to heightened lung capacity and greater oxygen intake.

Members of the species are physically stronger than humans, and some members of the species can communicate telepathically with certain sea creatures like whales.

Culture
The People of the Ocean are a highly advanced species capable of inter stellar travel and can generate technology than can cause earthquakes and floods. Despite these advancements their society is similar to an Iron Age or Roman society on Earth.

They have a royal family and governing body that has ruled for many years, though at the time of the series there was a civil war between those more militant members of the species and the rest of the population. The Queen is viewed as both a monarch and spiritual leader of the race.

History
Prior to the beginning of the series the aliens had recently managed to rebalance their ecosystem after years of industrial development had poisoned the Oceans. Despite this, it would be many years before the Oceans would be completely healed. Around that time their scientists first intercepted early transmissions from Earth into space.

The discovery of Earth sparked a large debate among the species; some felt the planet should be colonized while others thought the entire species should move there. When it was discovered that another sapient species was already inhabiting the planet it was decided that a diplomatic mission should be undertaken. The plan was to send an envoy to open negotiations with Earth. In return for teaching humanity how to use their oceans without damaging the ecosystem, the aliens would be allowed to take samples of Earth's waters and aquatic species back to their planet in order to speed their own world's recovery.