Zarth, Nature reserve in Treuenbrietzen, Germany.

Zarth is a roughly 262-hectare FFH nature reserve east of Treuenbrietzen's town centre, in the southwest of the Nuthe-Nieplitz Nature Park. Its western part is open grassland with the Alte and Neue Torfteich ponds, while the eastern Alt-Zarth section is wooded. Several spring-fed streams, including the Waldbach, Wendewasser, Kupferbach and Schwarzer Bach, flow from south to north.

The Zarth formed about 20,000 years ago at the end of the Weichsel glaciation, when retreating glaciers left a basin with a 200-hectare lowland forest and up to 4.5-metre-deep peat. In the 19th century farmers cut peat in the western part, drained the wet meadows for hay and named them Große Freiheit; the eastern wood, Alt-Zarth, supplied firewood and served as pasture. The first map depiction dates from 1780. In July 2007 a bird-protection committee bought about 95% of the area from the town of Treuenbrietzen.

The name Zarth comes from the Slavic tschert or cart, meaning devil, so locals call it Teufelswald. A memorial stone at the western entrance honours Eduard Prinke (1939–2013), the Jüterbog district deputy conservation officer who pushed for the area's protection.

A waymarked Landschaftstour path leads into the reserve from Treuenbrietzen or Bardenitz, and the Mühlentourroute 1 passes just south of the woodland. The wet meadows and spring-fed streams keep the ground soft, so wear waterproof footwear. A memorial stone near the western entrance honours Eduard Prinke (1939–2013), the Jüterbog district conservation official who pushed for the area's protection.

A memorial stone near the western entrance honours Eduard Prinke (1939–2013), deputy head of nature conservation in the Jüterbog district administration, who campaigned for the Zarth to be placed under protection. The reserve is also known locally as Teufelswald, or Devil's Forest, from the Slavic tschert or cart.