Aar Dam
The main dam and reservoir.
Location of Aar Dam in Germany
Country	Germany
Location	Lahn-Dill-Kreis
Coordinates	50°41′59″N 08°27′17″E / 50.69972°N 8.45472°E / 50.69972; 8.45472
Construction began	1984
Opening date	1991
Dam and spillways
Type of dam	Embankment, rock-fill
Impounds	Aar
Height (foundation)	15 m (49 ft)
Height (thalweg)	14 m (46 ft)
Length	270 m (890 ft)
Elevation at crest	272.5 m (894 ft)
Width (crest)	6 m (20 ft)
Dam volume	90,000 m3 (3,200,000 cu ft)
Spillway capacity	75 m3/s (2,600 cu ft/s)
Reservoir
Creates	Aartalsee
Total capacity	4,085,000 m3 (3,312 acre⋅ft)
Catchment area	60.5 km2 (23.4 sq mi)
Surface area	57 hectares (140 acres)
Normal elevation	270 m (890 ft)
Installed capacity	0.25 MW (340 hp)

The Aar Dam and its reservoir, the Aartalsee, lie in the upper Aar valley in the German state of Hesse. Both are in the municipalities of Bischoffen and Hohenahr in the county of Lahn-Dill-Kreis and about 15 km northwest of the town of Gießen in Hesse. On the lakeshores lie the villages of Ahrdt and Mudersbach, both part of the parish of Hohenahr. Since 1991 the dam has impounded the River Aar, a left-hand tributary of the Dill in the Gladenbach Uplands. The reservoir is also fed by the Stadterbach, Wilsbach (into the forebay), Weidbach and Meerbach (into the main reservoir).

The dam is primarily used for flood protection for the Aar and Dill. In Winter the reservoir is filled to a capacity of 1.33 million m³; in summer this rises to 1.84 million m³. Other uses are: raising low water levels, electricity generation, fishing and recreation. As a result, the dam and reservoir also contribute economically to the region. The reservoir was opened in 1992 as a bathing lake.

Its operator is the county council of Lahn-Dill-Kreis and the Dillgebeit Water Association.

• List of dams in Germany

• Hessisches Landesamt für Umwelt und Geologie: Der Aartalsee In: Badeseen in Hessen, retrieved 13 May 2009
• The Aartalsee
• Warum der Aartalsee entstand
• Photographs of the Aartalsee