Ferdinand Spring, Mineral spring in Mariánské Lázně, Czech Republic

Ferdinand Spring is a mineral water source located in Mariánské Lázně, a famous Czech spa town. The water emerges from the ground and is consumed by visitors seeking health benefits from its natural mineral content.

King Ferdinand I mentioned the salty springs in writing in 1528, the earliest record of a mineral spring in Mariánské Lázně. The name was settled by abbot Karel Kašpar Reitenberger after the spring was briefly called Kolovratův pramen. The Empire-style colonnade was built in 1826–1827 to Josef Esch's design on the abbot's initiative.

The spring's salty taste, from Glauber's salt, earned it the nickname Slaný. It was briefly called Kolovratův pramen after burgrave František Antonín Kolovrat-Libštejnský, who refused and proposed naming it Karlův pramen after abbot Karel Kašpar Reitenberger; the abbot instead chose the name of King Ferdinand I.

The spring is easily accessible on foot via marked pathways in the center of the spa town. Bring a cup or glass to drink the water, or purchase one from nearby vendors.

The shaft beside the spring releases vapours, apparently carbon dioxide, that can cause hallucinations; in 2019 the director Jan Kačena was poisoned after inhaling them. The spring's salty taste, compared to table salt, once earned it the nickname Slaný.