The proliferation of bloom-forming, harmful (toxic, food web altering) cyanobacteria (CyanoHABs)is attributable to human nutrient over-enrichment.Phosphorus (P) input reductions have been prescribed to control CyanoHABs, because P limitation is widespread and some CyanoHABs can fix atmospheric nitrogen (N2), thereby satisfying their nitrogen (N) requirements.However, eutrophying systems are increasingly plagued with non-N2 fixing CyanoHABs that are N and P co-limited or even N limited.Many of these systems are experiencing accelerating N loads, often exceeding rates of P loading.Therefore N and P input constraints are likely needed for long-term CyanoHAB control in such systems.Climatic changes, specifically warming, increased vertical stratification, salinization, and intensification of storms and droughts, play additional, interactive roles in modulating CyanoHAB frequency, intensity, geographic distribution and duration.This has complicated management strategies for control because CyanoHABs are capable of taking advantage of unprecedented levels of nutrient enrichment and regional and global climatic change, including warming and altered hydrology.Future climatic change scenarios, especially temperature increases and their physical-chemical-biological effects, will likely promote CyanoHABs.Management strategies should therefore incorporate climate change scenarios in the development of predictive bloom thresholds based on the interactions of nutrient enrichment, altered thermal and hydrologic properties of aquatic ecosystems.