Zantedeschia elliotianayellow calla lily. Information of Plantzafrica website leads me to believe that this is species Z. elliotiana, although I have been know to be wrong about these things. Photographed in a private garden in Berkeley, CA
2010.07.23 N Gnserndorf (bayou, 150 m AMSL).Flowering from may till september; here with Nuphar lutea.Not uncommon.German name: Schwimm-LaichkrautID: Fischer & al., Exkursionsflora (2008 3rd)