Microcystin-La is a toxin produced by blue-green algae in freshwater. It forms during algal blooms caused by nutrient pollution and warm temperatures.

Microcystin-La is one of several toxins produced by cyanobacteria, commonly known as blue-green algae. These organisms thrive in nutrient-rich freshwater bodies, especially during warm periods. As climate change increases water temperatures, algal blooms may become more frequent. Microcystin-La can be harmful if ingested, affecting the liver and other organs. Water utilities use specialized laboratory techniques to detect and measure microcystin levels, ensuring drinking water safety.