The East Prussia(n) plebiscite , also known as the Allenstein and Marienwerder plebiscite or Warmia, Masuria and Powisle plebiscite , was a plebiscite for self-determination of the regions southern Warmia (Ermland), Masuria (Mazury, Masuren) and Powisle, which had been in parts of the East Prussian Government Region of Allenstein and of West Prussian Government Region of Marienwerder, in accordance with Articles 94 to 97 of the Treaty of Versailles.