2-Methylisoborneol (MIB) is an organic chemical with a strong odor. It is a derivate of borneol. Its odor detection threshold is very low and it is one of the chemicals with major influence on the quality of drinking water. MIB is also a factor in cork taint in winemaking.
Some algae, particularly blue-green algae (cyanobacteria) such as Anabaena, produce MIB together with other odorous chemicals such as geosmin. They give a musty or earthy odor that can be quite strong if an algal bloom is present. Subsequent death of the cyanobacteria will also release MIB that is trapped in the cells. These chemicals can be smelled at very low levels, in the parts-per-trillion range (ppt range), and are responsible for many "taste and odor" issues in drinking water treatment and distribution. Cyanobacteria can also produce chemical toxins that have been a problem in drinking water in some cases.