Aquatic Vegetation and Control Measures 171 



whether this vegetable matter is a selected food or simply stuffing, taken 

 because other more desirable foods were not readily available. 



Dangerous Algae. Several species of bluegreen algae ( Cyanophycae ) 

 produce toxic substances when they die and decay. These algae have 

 been responsible for mammalian, avian, and fish deaths.''^ The genera in- 

 volved in these deaths were Aphaiiizomenon, Anabaena, Nodiilaria, 

 Coelosphaeriiim, and Glaeotrichia. These algae are particularly dangerous 

 when they appear as "blooms" on lakes and ponds and are concentrated 

 by wind action along the downwind lake margin. Domestic stock drinking 



Figure 6.12. Floating mats of filamentous algae are a 

 nuisance to boaters and swimmers and make fishing nearly 

 impossible. 



this concentration of water and bluegreen algal cells rapidly show signs 

 of acute poisoning. The toxic substance produced by the cells will cause 

 the death of animals when algal cells are themselves excluded, and will 

 survive the equivalent of water treatment using alum coagulation, filtra- 

 tion, and chlorination. However, as far as is known, no human deaths or 

 outbreaks of human gastroenteritis have been positively traced to these 

 algae, although unexplained outbreaks of gastroenteritis have been re- 

 ported in the same areas where extensive algal blooms were present.^^ 

 Nuisance Algae. Most filamentous algae are considered nuisance plants 

 because they eventually rise to the water surface and float about as green 

 "slime" or "scum" until they die and disintegrate (Figure 6.12). In this 

 position they are obnoxious to swimmers, and foul motor blades, oars, 

 and lines of boaters and fishermen. 



