Lake Stymphalia, Mountain lake in Sikyona Municipality, Greece

Lake Stymphalia sits at roughly 600 meters elevation in northeastern Peloponnese, with a rectangular shape and marshy reed-filled areas edging its shores. Water levels shift dramatically across seasons, and the lake's depth varies considerably throughout the year.

The Arcadian city of Stymphalos stood near the lake's shores. In Roman times the emperor Hadrian built an aqueduct that supplied Corinth with water from the lake, as the Greek Wikipedia article on Stymphalia records.

The lake is tied to Heracles' sixth labour: the Stymphalian birds infested the Arcadian woods near the water, and Athena gave him bronze clappers to drive them from the dense vegetation before he shot them with arrows. The ancient Arcadian city of Stymphalos stood near the shores.

The lake lies in a closed karst basin at about 600 m elevation between Mount Kyllini and Mount Oligyrtos. Water covers the basin mainly in winter, reaching 3.5 km², while in early autumn the depth drops to about half a metre. The surrounding ground is usually fairly dry underfoot, but in damp weather thousands of small green frogs hide in the grass and jump aside as you walk.

The lake's ecosystem was already famous in ancient times for its bird populations, long before modern ornithology made it a focus of scientific study. This long history of avian interest connects old legends with today's understanding of the region's ecology.