Microcystin-LW is primarily known for its role as a potent hepatotoxin produced by certain strains of cyanobacteria, especially Microcystis aeruginosa, during harmful algal blooms in freshwater systems. Its main significance lies in environmental and public health monitoring, where it serves as a critical indicator for water quality assessment. Due to its high toxicity and stability in water, it is a key compound analyzed in drinking water and recreational water safety testing. It is also used in scientific research to study liver cell toxicity, protein phosphatase inhibition, and cellular oxidative stress mechanisms. Because of its specific action on protein phosphatases 1 and 2A, it helps researchers understand signal transduction pathways and the role of phosphorylation in cell regulation. Additionally, Microcystin-LW is employed as a reference standard in analytical chemistry for the detection and quantification of microcystins in environmental and biological samples using techniques such as HPLC and LC-MS. Due to its toxicity, it has no commercial or industrial applications and is strictly handled under controlled conditions for research and monitoring purposes.