Litheos Potamos (Lethean River) collects water from the basin of Gergeri and Panassos in the south-eastern roots of Psiloritis. It continues its course as a wide river from Apomarma, during which many vertical streams meet the main stream. Throughout its course one meets many dilapidated watermills and the ancient aqueduct that transferred water from Gergeri to Gortyn.
Shortly before ancient Gortyn, the stream meets soft limestone and turns into the Gorge of Litheos, that passes beneath the acropolis of Gortyn. The canyon can be crossed by a trail coming along the west side of the gorge. In ancient Gortyn, the gorge turns back into a flat river, passes next to the evergreen plane tree of Gortyn and crosses the ancient city. Then it flows through the village Mitropolis (so it is also known as Mitropolianos River) and finally empties in river Geropotamos.