Salt water

From Creatures Wiki

Creatures 3 has two types of water: fresh water and salt (Creatures 2 has only one type, Creatures 1 technically has none!). Most fish can only survive in one type of water, with the known exception of the pirahna being able to live in both.

An example of salt water is the water in the Aquatic Terrarium. Examples of fish that can survive only in salt water are the Rainbow Sharkling.