Delfzijl (Dutch pronunciation: [dɛlfˈsɛil]; Gronings: Delfsiel) is a city and municipality with a population of 25,651 in the province of Groningen in the northeast of the Netherlands. Delfzijl was a sluice between the Delf and the Ems, which became fortified settlement in the 16th century. The fortifications were removed in the late 19th century.