In the Cuban context, the elements connected to cyanotoxin incidence and societal effect, with understanding and risk perception being the most critical difficulties, are not fully known. The goals of this study were to estimate the risk extension and microcystin-LR levels in 24 water reservoirs in eastern Cuba, as well as to investigate the environmental conditions that promote toxic cyanobacteria growth and microcystin-LR occurrence. Sampling was done in the early morning hours, within situ determination, and physicochemical analysis was done in the lab. Microcystin-LR levels in water and within cells (intracellular toxins) were evaluated by UPLC–MS analysis following solid-phase extraction. Eutrophication was discovered in the reservoirs tested, with high levels of TN: TP ratio and phytoplankton cell densities, high water temperatures, and low transparency, resulting in collateral effects such as cyanobacterial bloom and microcystin-LR occurrence. Concentrations of MC-LR more than the WHO limit for drinking water (1 gL1) were identified in the reservoirs of Hatillo, Chalons, Parada, Mcara, Baragua, Cautillo, La Yaya, Guisa, and Jaibo.
