Worldwide, excessive nutrient loads in lakes and reservoirs have led to the rapid increase of harmful cyanobacteria. Blooms of these algae block the use of surface water for drinking, irrigation and recreation. Climate change is expected to further increase the frequency, duration, and magnitude of cyanobacterial blooms. Aquatic ecologists from NIOO are busy gaining more detailed insights into cyanobacterial blooms across scales, in future climates and in respect to toxicity.