Lake Lysimachia, Natural lake and Special Protection Area in Agrinio Municipality, Greece.

Lake Lysimachia is a natural body of water in Agrinio Municipality covering roughly 13 square kilometers with a maximum depth near 9 meters. Water flows in from the Ermitsa River and connects to nearby Lake Trichonida.

The two lakes, Lysimachia and Trichonida, were once fully joined in a single wetland, as travellers of the 19th and early 20th centuries recorded, surrounded by nearly impassable forest. After the old Antirrio–Ioannina national road was built between them and irrigation works followed, the lakes kept contact only through a controlled canal. The Ermitsa torrent feeds Lysimachia, which drains through the Dimikos into the Acheloos.

The lake's name comes from Lysimachus, a general under Alexander the Great. The 19th-century travellers who crossed the Aetolian plain recorded dense, nearly impassable forests around the two lakes before the old Antirrio–Ioannina road was built between them.

The old Antirrio–Ioannina national road runs between Lake Lysimachia and Lake Trichonida, giving direct road access; Agrinio lies 6 km northeast. The two lakes now connect only through a controlled canal, so the shoreline is best followed on local roads. Water enters from the Ermitsa stream and leaves via the Dimikos toward the Acheloos.

The lake serves as a vital resting point for migratory birds making their seasonal journeys across Europe. Its stable water levels are maintained through its connection with the neighboring Lake Trichonida.