Bostalsee, Recreational reservoir in Nohfelden, Germany.

Bostalsee is a reservoir in Nohfelden in the northern Saarland, held back by a 500-metre dam and covering 120 hectares at about 400 metres above sea level. Its maximum depth is 18 metres. The photograph shows dark blue water dotted with small white boats, curved wooden docks on the western and southern shores, and a cluster of buildings beside a patterned parking area.

The Bostalsee was dammed in 1979. The project was initiated in the early 1970s by Werner Zeyer, then head of the St. Wendel county council and later minister president of the Saarland, to strengthen tourism and local recreation; the previous landowner was expropriated. The dam impounds the Bos and the Dämelbach. Repairs to the dam wall ran from October 2007, and the lake reopened in March 2009.

The reservoir takes its name from the Bos and Dämelbach, the two streams it impounds; the villages of Bosen, Eckelhausen, Gonnesweiler and Neunkirchen/Nahe border its shores. The lake is the end point of the Straße der Skulpturen, the sculpture road that begins in St. Wendel. Motor boats are banned apart from a few electric craft and rescue boats, so sailing, surfing, pedal boating and angling dominate the water.

A 6.8 km walking path and a 7.2 km cycle path circle the lake, passing the villages of Bosen, Eckelhausen, Gonnesweiler and Neunkirchen/Nahe. Motor boats are banned apart from a few electric craft and rescue boats. The south-western section is a nature reserve, so visitors keep to the marked routes there.

Since late 2013, water released from the reservoir has driven a small hydropower unit, and the electricity it produces is used mainly to light the 6.8 km circular walking path around the lake during the winter months. The dam that holds the water back is 500 metres long.