Microcystin-LR is primarily known as a potent hepatotoxin produced by certain strains of cyanobacteria, commonly found in freshwater ecosystems during algal blooms. Its main significance lies in environmental and public health monitoring due to its high toxicity when present in drinking water supplies. It serves as a key indicator in water quality testing, helping regulatory agencies assess risks associated with cyanobacterial contamination in reservoirs, lakes, and drinking water treatment systems. Due to its stability and toxicity, microcystin-LR is used in research to study liver damage mechanisms, particularly hepatocyte apoptosis and disruption of protein phosphatases 1 and 2A. It is also employed in toxicological studies to evaluate detoxification methods, including the efficiency of water treatment processes such as ozonation, UV irradiation, and activated carbon filtration. Additionally, it plays a role in the development and validation of detection methods like ELISA, PCR, and mass spectrometry for early warning systems in environmental monitoring. Because of its biological activity, it is sometimes used in laboratory settings to induce oxidative stress and study cellular defense pathways. However, it has no commercial or therapeutic applications due to its high toxicity.