The majority of the ponds on Hampstead Heath are fed by the headwater springs of the River Fleet. Three of the main ponds are now large freshwater bathing/swimming ponds: two designated single sex (male/female Highgate no. 2 and Highgate no. 5 respectively); and one for mixed bathing (Hampstead no. 3). The bathing ponds are not the only special-use ponds, however: Highgate no. 3 pond is the Model Boating Pond and it, along with a few other ponds, are open to anglers. A number of the other ponds are set aside as wildlife reserves or are purely ornamental (such as the more minor Viaduct Pond). The City of London Corporation tried to close the bathing ponds in 2004, but a challenge at the High Court by swimmers overcame this, though charges for swimming were introduced.