The Alpheios (Greek: Αλφειός, Ancient Greek: Ἀλφειός, Latin Alpheus), sometimes spelled Alfeiós, is the main stream of the Alpheios Valley drainage system, a dendritic type, originating on the north slopes of Mount Taygetus, located in the center of the Peloponnesus of Greece, and flowing to the northwest to the vicinity of Olympia, where it turns to the west and, after being impounded by the Flokas Dam, a hydroelectric facility, empties into the Gulf of Kyparissia of the Ionian Sea south of Pyrgos.

The entrance into the gulf through agricultural land and across an unpopulated, sandy beach partially blocked by a spit is hydrologically unspectacular, with the water too shallow to be navigable by any but the smallest craft.

The concept of a single source has little meaning for most of the rivers of Greece, which begin as a confluence of multiple springs in the mountain valleys.

Most recently attempts have been made to connect the Alpheios through underground channels to the "40 rivers" region of the high plateau of central Arcadia (around Tegea and Mantineia, etc.).

It has been necessary to establish regular monitoring by the government and create substructure to make important decisions concerning the fate of the river.

On the left is the long ridge of Mount Lykaion, relatively uneroded, suggesting that different types of rock occur on either side.

The entire southwest Peloponnesus is split from Arcadia by this great trough, considered two basins, which must have been in place in some form before any extensive dendrism.

Scarps along the trough suggest that the two basins are rift valleys, depressions, or graben, caused by the ridges on each side moving away from each other.

The Hellenic Center for Marine Research (HCMR) therefore added the study of water quality in Greece to its previously existing AQEM program.

Select river sites were monitored for three seasons of 2000–2001, spring, summer, and winter, the results appearing in an online report of 2005.

[10] It is theorized that these ridges are their own types of rock because they represent separate microcontinents that migrated across Tethys Sea from Gondwana and docked against Eurasia during the compressional regime of the Hellenic orogeny, a branch of the Alpine orogeny, when parts of the African plate were being pushed against the Eurasian plate and being subducted under it.

The isotopic zones are a product of the Continental drift theory and its modern development, plate tectonics, which prevailed after 1958.

Mathematical hydrology requires definite numbers: rivers have lengths, cross-sections, measurable linear and volumetric (discharge) rates of flow.

Intermittent dendritic streams come from higher, but there is no evidence that they follow any tunnel through the Mainalo Mountains to trickle out as springs at this or that lower location.

[18] Megalopolis sits on the high point of the central valley, while the Alpheios, sourced in the southeast, skirts the hill to the south, the west, and exits to the NW dropping through a steep and impassible gorge.

A former defense against enemies on foot, the gorge is popular for its recreational rafting over rapids,[19] justifying the ancient etymology of "whitewater."

In 1969 the Megalopoli power company opened a lignite-burning facility to the NW of the city on the right bank of the Alpheios, finishing two plants in 1970 and one in 1975.

To obtain the lignite, they began strip-mining the region to the west of the city, working the mine southward, then eastward.

The source of the river is on the southeast of the mine in the district still called Anthochori ("flowery place"), once a pleasant village, and still advertised as that in the media.

The crossing points are marked by V-gullies located 1 to 2 km from the morass: one due south, two west, one NE, and one N from Megalopoli through the mine.

These streams are in the small tributary category, some mere thicketed ditches, others with pebble beds and forested banks cutting across the rolling upland.

The generally preferred candidate for the title of upper Alpheios drops through the 400 m (1,300 ft) elevation line at 37°22′35″N 22°08′53″E / 37.3763095°N 22.1481159°E / 37.3763095; 22.1481159 as it crosses under Rt.

From the road[23] the river appears as a deep V-shaped ditch lined densely with trees over which a plank walkway has been placed.

Above the 400 m line the stream drops in a long flow across the base of the Mainalo Mountains from the valley leading up to Tripoli on the high plateau.

There is nothing like a source in the entire upper valley, but if there were, it is clear that it wouldn't be located in the villages of Asea or Dorizos perched on the mountain ridges.

Those names are simply convenient hooks on which to hang a source imagined to be there by offsite geographers looking for a mystic connection to Tripoli.

In Greek mythology, the Peneus and Alpheus were two rivers re-routed by Heracles in his fifth labour in order to clean the filth from the Augean Stables in a single day, a task which had been presumed to be impossible.

In the Aeneid, Virgil describes the Alpheus as flowing under the sea to resurface at Ortygia on Sicily, or "so runs the tale".

[24] The nymph Arethusa, who was transformed into a fountain, was called Alpheias because it was believed that her stream had a subterraneous communication with the river Alpheius.

[25] The river disappears several times into the limestone Arcadian mountains and reemerges after flowing some distance underground.