Chrysosporum bergii is a bloom-forming cyanobacterium in the order Oscillatoriales, recognized for its ability to produce cylindrospermopsins — potent hepatotoxic alkaloids that pose risks to human and animal health when present in drinking water or recreational water bodies. The species has been documented causing toxic blooms in lakes and reservoirs in Europe, South America, and Australia. In northern Europe, including Sweden, C. bergii blooms have occurred in warm, stratified lakes with elevated phosphorus concentrations. The species is characterized by straight or slightly curved filaments (trichomes) that aggregate into macroscopically visible scums at the water surface during bloom events. Cylindrospermopsins produced by C. bergii inhibit protein synthesis and can cause liver damage, kidney failure, and other systemic effects in mammals, birds, and fish exposed to sufficient concentrations. The proliferation of this species and related cylindrospermopsin producers worldwide is linked to climate warming and lake eutrophication, as warmer temperatures and higher nutrient loads favor their competitive success over other phytoplankton groups. The conservation status of C. bergii has not been evaluated by the IUCN; it is listed as Not Evaluated.