​OBRA, a river of Germany, in the Prussian province of Posen, a left-bank tributary of the Warthe. It rises near Obra, N.W. from Koschmin, and forms in its course marshes, lakes and the so-called Great Obrabruch (fen). The latter, 50 m. long and about 5 m. broad, is a deep depression in the undulating country of south-west Posen. The river is here dammed in and canalized and affords excellent water transit for the agricultural produce of the district.