The increasing occurrence of toxic freshwater cyanobacteria blooms in marine or brackish waters, coupled with elevated cyanotoxin concentrations in marine life, poses an emerging threat to human health. These events are often associated with temperature, salinity and the eutrophication of affected areas, however global changes causing extreme events can cause rapid shifts in their dynamics and subsequent propagation. This systematic review presents reports from 2010 to 2024 where the main objectives were to describe (i) worldwide occurrence of freshwater cyanobacteria toxins in transitional waters
(ii) global changes and shifts in cyanobacteria dynamics and (iii) patterns of the cyanotoxins microcystins, nodularins, saxitoxins, cylindrospermopsin and anatoxins in marine organisms. PRISMA ("Preferred Reporting Items for Systematic Reviews and MetaAnalyses") protocol was used, and literature search was done using two databases (PubMed and Web of Science) to summarise the research outcomes. The higher number of events was reported in the USA (west coast and east coast), followed by the Baltic Sea. Both Mediterranean and Atlantic coasts of Europe had experienced the severe impact of these events in coastal and brackish environments. Locations in South America, Africa and Asia have also been affected. Despite the lack of consensus for cyanotoxin guidelines, the highest values of the most common cyanotoxins accumulated in marine organisms were in bivalves (microcystins) and in fish (nodularins), with values largely exceeding the existing guideline of 51 μg cyanotoxins.kg