• As primary producers, algae are most directly affected by 

 physical and chemical factors, such as temperature, 

 nutrients, and toxins; 



• Sampling is quick, easy and inexpensive, and causes minimal 

 damage to resident biota and their habitat; 



• Standard methods and criteria exist for evaluating the 

 composition, structure, and biomass of algal associations; 



• Identification to species is straightforward for the 

 diatoms, for which there is a large body of taxonomic and 

 ecological literature; and 



• Excess algae in streams is often correctly perceived as a 

 problem by the public. 



Periphyton is a diverse assortment of simple photosynthetic 

 organisms called algae, and other microorganisms that live 

 attached to or in close proximity of the stream bottom. Most 

 algae, such as the diatoms, are. microscopic . Diatoms are 

 distinguished by having a cell wall composed of opaline glass- - 

 hydrated amorphous silica. Diatoms often carpet a stream bottom 

 with- a slippery brown film. 



Some algae, such as the filamentous greens, are conspicuous 

 and their luxuriant growth may be aesthetically undesirable, 

 deplete dissolved oxygen, interfere with fishing and fish 

 spawning, clog irrigation intakes, and cause other problems. 



The federal Clean Water Act directs states to develop water 

 pollution control plans (Total Maximum Daily Loads or TMDLs) that 

 set limits on pollution loading to water-quality limited waters. 

 Water-quality limited waters are lakes and stream segments that 

 do not meet water-quality standards, that is, that do not fully 

 support their beneficial uses. The Clean Water Act and USEPA 

 , regulations require each state to (1) identify waters that are 

 water-quality limited, (2) prioritize and target waters for 

 TMDLs, and (3) develop TMDL plans to attain and maintain water- 

 quality standards for all water-quality limited waters. 



