The Oste (, also ) is a river in northern Lower Saxony, Germany with a length of 153 km, left tributary of the Elbe. It flows through the districts of Harburg, Rotenburg, Stade and Cuxhaven and empties into the Elbe river near Otterndorf. Its drainage area is 1.711 km² and the decline between the source and the estuary is 31 m. Tributaries are Ramme, Aue, Twiste, Bade, Bever and Mehe.