Gretagrund (or Greta-Grund) is a shoal located a few km southeast of Ruhnu island in the Gulf of Riga, Estonia.
Since 12 August 2010 the water area was taken under protection as being a habitat for the following migratory birds: Black-throated loon (Gavia arctica), little gull (Larus minutus), red-throated loon (Gavia stellata), long-tailed duck (Clangula hyemalis), velvet scoter (Melanitta fusca) and razorbill (Alca torda). During a survey in 2008, Paramysis intermedia (from genus Paramysis) was found in Gretagrund as a new species in the Baltic Sea.