Rüstringen or Rustringen was an old Frisian gau which lay between the modern district Friesland

Friesland (district)

Friesland is a district in Lower Saxony, Germany. It is bounded by the districts of Wesermarsch, Ammerland, Leer and Wittmund, and by the North Sea...

 and the Weser river in modern Lower Saxony

Lower Saxony

Lower Saxony is a German state situated in north-western Germany and is second in area and fourth in population among the sixteen states of Germany...

. Nowadays, only a small part of the original territory remains, namely the Butjadingen

Butjadingen

Butjadingen is a peninsula and municipality in the Wesermarsch districts, in Lower Saxony, Germany.-Geography:Butjadingen is situated on the German North Sea coast. It is bordered on the west and southwest by the Jade River and on the east by the Weser River. It forms the northern part of the...

 peninsula. The largest part of historical Rüstringen has been lost to the sea in the Middle Ages due to various storm surge

Storm surge

A storm surge is an offshore rise of water associated with a low pressure weather system, typically tropical cyclones and strong extratropical cyclones. Storm surges are caused primarily by high winds pushing on the ocean's surface. The wind causes the water to pile up higher than the ordinary sea...

s and now forms the Jadebusen

Jadebusen

The Jade Bight, is a bay on the North Sea coast of Germany. It was formerly known simply as Jade or Jahde.About 180 km² in area, the Jade was largely created by storm floods during the 12th and 16th centuries. During this period it was connected in the East to the river Weser...

 bay.

Butjadingen and Rüstringen