The longest river is the Alfeios. Other rivers are the Erymanthos, Pineios and Neda. Alfeios, Pineios and Neda flow into the Ionian Sea in Elis. Less than 1% of the prefecture is open water, most of it found in artificial reservoirs and dams, in the north and east. The Pineios Dam supplies water for Northern Elis. The water is not safe for drinking, because it contains some contaminants. A second, smaller reservoir in the river Alfeios near Olympia and Krestena supplies water to Pyrgos.