Toxic cyanobacteria form mass occurrences in fresh and brackish water bodies worldwide. They cause animal poisonings and pose a serious health risk for humans. We have shown in previous studies that toxic mass occurrences of cyanobacteria are common in Finnish lakes and in the Baltic Sea. Neurotoxic and hepatotoxic cyanobacteria are found in freshwater bodies while only hepatotoxic blooms occur in the Baltic Sea. We developed molecular tools to detect toxins and odorous metabolites producing cyanobacteria. Understanding why and how toxic blooms develop helps protect water bodies and water users. Cyanobacteria are also a prolific source of novel bioactive compounds containing anticancer, antifungal, antiviral and antibacterial activities. We maintain the UHCC culture collection of cyanobacteria. This collection provides model strains to study cyanobacterial phylogeny, physiology or ecology. It also serve as a renewable source for discoveries of bioactive compounds and their biosynthesis through genome mining.