Dornumersiel is an East Frisian village and coastal resort on the Wadden Sea coast in Lower Saxony, Germany.

The two settlements are only divided by Dornumersieler Tief, the historical border of Norderland and Harlingerland.

[2] Dornumersiel is located directly on the Wadden Sea coast south of the island of Langeoog.

The sluice (Siel) village is one of the oldest harbors on the East Frisian coast.

After the St. Peter's flood on 22 February 1651 destroyed another sluice village on the coast, later known as Altensiel, the Dornumer and Westeraccumer Siel were built right next to each other in 1653.