Helmbachweiher, Reservoir in Elmstein, Germany

Helmbachweiher is a reservoir in the Palatinate Forest near Elmstein, created by damming the Kohlbach stream. The water body covers roughly 0,6 hectares and reaches a maximum depth of about 2 meters with clear water.

The reservoir was created in 1970 by damming the Kohlbach, a forest stream that passes the dam at the lake's end and flows into the Helmbach a few steps further on. Both sides of the Kohlbach mouth were raised along roughly 100 metres of the Helmbach's right bank to serve as the impoundment structure. In its origin it is comparable to the medieval woogs.

The lake's main role is as a Kneipp water-therapy pool, a practice named after Bavarian priest Sebastian Kneipp. Its water quality was rated "excellent" by the European Union in 2014, and green algae of the genus Water net, found only in unpolluted water, have been recorded here. Swimmers and waders use the long wooden footbridge to enter the water.

A forester's lodge and educational garden are located near the water and make it easy to access. There are also barbecue areas for visitors who want to spend time by the water.

The name is misleading: the reservoir is fed by the Kohlbach, not the Helmbach that flows a few metres away, and older texts sometimes get this wrong. The Kohlbach passes the dam at the lake's end and joins the Helmbach just steps further on.