A large amount of suspended solids—fine particles floating in the water—can directly affect fish by clogging their gills, changing their behavior, lowering their resistance to disease, and blanketing gravel streambeds needed for spawning. Suspended solids can smother freshwater mussels, which are valuable for water filtering. They can make the water appear murky and affect the aesthetic enjoyment of the rivers and safety for swimmers. Suspended solids may be fine soil particles common in stormwater runoff, organic particles including bacteria and algae, or fine particles discharged with wastewater. Suspended Solids scores are calculated based on a comparison with published statistics for similar ecoregions.