Where is Cabomba sometimes used for decoration but also utility?

Context: Cabomba is an aquatic plant genus, one of two belonging to the family Cabombaceae. It has divided submerged leaves in the shape of a fan and is much favoured by aquarists as an ornamental and oxygenating plant for fish tanks. Use in the aquarium trade has led to some species being introduced to other parts of the world, such as Australia, where they have become weeds.

Answer: fish tanks