The city of Barcelona has no longer any natural ponds within its confines, and the ponds that do exist are artificial and ornamental in function. Some are more natural (e.g. the ponds in Diagonal Mar) and others more artificial (e.g. in Parque de la España Industrial or in Parque de la Creueta del Coll).
Most interesting because of their size and biological variety are the ponds in Parque de la Ciudadela and Diagonal Mar. In the latter, a few waterbirds such as mute swans (Cygnus
olor), common geese (Anser anser) and tufted ducks (Aythia
fuligula) have been introduced.