Harmful algal blooms caused by cyanobacteria (cyanoHABs) are a serious water quality problem in Iowa’s lakes. The presence of cyanobacterial toxins in Iowa’s lakes can threaten human health and increase economic loss. The proposed study will investigate how co-nutrient limitations, such as nitrogen and iron, combine with factors such as temperature and dissolved oxygento fuelcyanoHAB growth and toxin release across different lake types in Iowa. In general, artificiallakes tend to havelowernutrients, but earlier studies found nutrient conditionsto be higher in those surrounded by agricultural land use. We hypothesize that cyanoHAB intensityis higher in Iowa’s artificial lakes (e.g. reservoirs, impoundments) due to greater surface runoff carrying agriculturally-derived nutrients (N, P). We will test this hypothesis by measuring nutrients, including iron (Fe), which is generally not measured. We willlook for correlates between individual nutrients or nutrient ratios and/or physical conditions with phytoplankton biomass and toxin presence. This approach will help reveal larger landscape-scale trends distinguishing the susceptibility of artificial vs. natural lakes to cyanoHAB formation and toxin release. Findings from this study will help facilitate environmental risk management and develop mitigation strategies to reduce human and animal health risk.