This book is a result of the research that has been conducted on the Department of the Freshwater Conservation of the Brandenburg University of Technology Cottbus-Senftenberg, Germany. It tries to explain an unusual phenomenon of the late summer/autumnal blooming of the green alga Autumnella lusatica sp.nov. in the acidic mining lake Halbendorf situated in the acidic mining lake region of Lusatia, east part of Germany.