Under normal conditions, cyanobacteria are present at low levels and play an important role in aquatic ecosystems. When HCBs occur, cyanobacteria become visibly abundant can look like grass clippings, blue-green scum, or spilled paint on the water surface. HCBs may also be suspended in the water column or attached to rocks, sediments or plants on the bottom of the waterbody. To view photos of harmful cyanobacterial blooms found in Wyoming, click here.