Naturschutzgebiet Oberwaldsee von Dietesheim, Nature reserve near Dietesheim, Germany

The Oberwaldsee von Dietesheim nature reserve is a protected area near Mühlheim am Main that spans forest and meadow landscapes. Several lakes with deep blue water shape the terrain, formed from old basalt quarries, while dense trees line the edges.

The Oberwaldsee von Dietesheim reserve was designated in 1985, after a biotope survey that year established its geological, landscape, zoological and botanical value. Its lakes are flooded former basalt quarries on the Steinheimer Terrasse, and the protection order also targeted illegal recreational use and afforestation of the remaining sandy dry grasslands.

The reserve's dry grasslands are home to the Rostbraunes Ochsenauge butterfly (Pyronia tithonus), a warmth-loving species found at only a few dry, warm spots in the Rhine-Main region. The lakes' shores serve as breeding grounds for Little Grebes, Great Crested Grebes and Tufted Ducks.

The reserve lies southeast of the Dietesheim district on the Steinheimer Terrasse, in the Untermainebene natural region. The 1985 biotope survey recorded illegal recreational use and afforestation of the sand dry grasslands as disturbances, so staying on paths protects the dry lawns and shore zones where grebes and Tufted Ducks nest.

The reserve is home to rare bird species like Black Kites and Wrynecks that can be spotted along the walking paths with patience. Specialized butterfly species also live in the dry grasslands, found nowhere else nearby.