Lake and channel shores are covered with vegetation typically found in swamps, mostly consisting of reeds and rushes. The marshy ground by the shore is characterised by a plant community of salt-tolerant pioneer species, known in Italian as "salicornieto".
Plenty of water birds are to be found in Circeo National Park's lakes and marshes: over 260 species, both nesting and migratory/wintering. The Park's coastal lakes are Latium's main wintering site for water birds, with a peak of 23,400 birds (data from 2006).
Being located along the main migratory routes, the Park is especially well placed for many bird species to stop, and take advantage of the food they find in wetlands along the coast. The Park, in particular, represents a rest stop both for birds migrating across Italy in a NE-SW direction (a typical phenomenon in Central Italy) and for those migrating along the peninsula's coastline.
Among birds in the Park's wetland we find Anatidae such as mallards, gadwalls, widgeons, pintails, northern shovelers, pochards, and ferruginous ducks. Coots, too, are very numerous in this area (over 10,000 animals).
The colony of wintering great cormorants is the largest in peninsular Italy. Nesting species, instead, include little grebe, little bittern, mallard and moorhen.
Beside coastal lakes (Lakes Paola, Caprolace, Monaci and Fogliano) and wild wetlands (Pantani dell'Inferno), other important environments for migratory birds are the Circeo Promontory and the Island of Zannone.