This document discusses harmful algal blooms (HABs) in freshwater systems like ponds. It begins by describing the organisms responsible for HABs, cyanobacteria, and some of the major genera commonly found in Ohio waters. The document then discusses what causes HABs, primarily an overabundance of phosphorus in the water leading to excessive growth. This is followed by outlining concerns with HABs, including impacts to water quality, potential toxins produced that can harm animals and humans, and off-flavor compounds that affect taste. The document concludes by noting several cyanobacterial genera common in Ohio and the types of toxins they may produce.