Algal blooms of the 18th and 19th centuries.

Algal blooms, including those containing cyanobacteria, are of environmental concern due to the toxicities of some of the constituent microorganisms. This compromises the safety of freshwater causing illness in livestock and humans. We present historical accounts of algal blooms occurring during the 18th and 19th centuries indicating that the advent of intensive farming in the 17th century provided nutrients for promoting harmful algal blooms.