Parque da Cidade has several bodies of water, but only one is affectionately called "Charco Maravilha"! Among other reasons, it is home to the only known population of the black-winged toad around Porto. We could say that this little frog, famous for its black toenails on its hind legs, is the flagship species of Porto's amphibians. The challenge for this session is to find out who the other neighbours are and the reason for the "black toenail" of its most famous inhabitant.