Berezan (Cyrillic: Березáнь; Ancient Greek: Borysthenes; former ) is an island in the Black Sea at the entrance of the Dnieper-Bug Estuary, Ochakiv Raion, Mykolaiv Oblast, Ukraine. It is often being confused with the artificial island of Pervomaisky that is located within Dnieper-Bug Estuary. The Berezan island measures approximately 900 metres in length by 320 metres in width. It is separated from the mainland (to which it may have been connected long ago) by about a mile and a half of shallow water.