Smraďoch, Nature reserve near Mariánské Lázně, Czech Republic.

Smraďoch is a nature reserve on the edge of Mariánské Lázně in the Czech Republic, where gas vents at the surface release hydrogen sulfide from underground fissures. These vents form small geyser-like structures called mofettes, which are scattered across the protected ground.

The area was granted official protection in November 1968, after its geological value was recognized in connection with regional tectonic activity. That recognition made it possible to protect the underground structures and the habitats that depend on them.

The reserve's name comes from the strong hydrogen sulfide smell that carries far from the mofettes. The plants growing here include round-leaved sundew, common butterwort, cranberry, black crowberry, Fuchs' orchid and whorled Solomon's seal, several of them protected species.

A wooden boardwalk runs through the reserve and is easy to walk for most visitors. Information panels along the route explain the geological and botanical features of the ground.

The reserve covers 7.9 hectares, and only a small part of the forest peat bog is accessible on the plank walkways. The bog drains through the Mnichovský potok and Pramenský potok streams into the Teplá river.