The largest inland marsh in Italy stretches south from Monsummano towards the Arno valley — around 1,800 hectares of reedbeds, water channels and seasonal pools, recognised as a Site of European Community Importance. The marshes are a key wintering ground for herons, egrets, ducks and the occasional flamingo, and in spring host nesting purple herons and night herons.
The Centro di Ricerca Documentazione e Promozione del Padule di Fucecchio at Castelmartini runs guided walks and maintains observation hides. Bring binoculars and insect repellent in summer. October to March is the best birdwatching window, with the autumn rains filling the marshes after the dry summer.