An algal bloom was investigated on Back River on September 12^th showed extremely high densities of the blue-green algae Microcystis aeruginosa in the surface waters of the river. Concentrations of Microcystis in the surface scum were measured at 1.2 million cells per milliliter and 169,600 cells per milliliter just 1 meter below the surface. Earlier this summer on August 16^th, DNR investigated reports of surface blooms on the river but densities were significantly less at concentrations of 164,376 cells/ml, considered to be a moderate bloom.