Over a hundred carbonic mineral springs are found in Mariánské Lázně and its surroundings. 53 of them are used, most of them are ferrous acidulous waters of different chemical composition. Six main springs are used for drinking treatment: Křížový, Rudolfův, Karolinin, Lesní and Ambrožův. Mariin spring, which gave the town its name, is a carbonic gas spring. The springs and their healing effects were well known to inhabitants of the local villages even before the spa was founded.