The Plankton Algae of the Palisades Interstate Park 135 



each of the two vessels, one of which now contains i part of copper 

 sulphate to one million parts of water and the other contains untreated 

 water. If the fish die in less than 24 hours in the copper sulphate 

 solution and not in the control, it is evidence that the chemical solu- 

 tion was too strong and a second trial should be made, using a frac- 

 tional part of an ounce of the standard copper sulphate solution to 10 

 gallons of water (the resultant solution would of course contain a 

 corresponding fraction of a part per million of copper sulphate). 

 If the fish in the experimental solution, however, did not die, then this 

 strength of copper sulphate solution can be used for the eradication 

 of the algae without killing the fish." 



In July, 1 91 8, in Carr Pond in the Palisades Interstate Park, the 

 algae became so abundant and were such a nuisance that an effort was 

 made to adopt control measures. The Park Commissioners there- 

 fore sought permission of Mr. Geo. D. Pratt, State Conservation 

 Commissioner, Albany, to use the copper sulphate method for killing 

 the algae, to which he replied on July 19 : " You are authorized to 

 use in Carr Pond commercial copper sulphate, ratio one part dry 

 weight of copper sulphate to 5 millions parts of water. Rag bags 

 filled as above so that applications be distributed uniformly." 



Under this authorization five park workmen, under my direction 

 on July 22, 1918, made the treatment (figure 19). The estimate of 

 the volume of the lake was furnished by the office of the Chief 

 Engineer of the Park. Since the organism causing the bloom was 

 Anabaena the maximum concentration permitted was not used for 

 its eradication. Soon after the application of the copper sulphate the 

 color of the water turned from a grass-green to a lighter bluish shade, 

 because of the killing of the algae. After the copper sulphate had 

 been in the lake for 24 hours many fish were seen at the surface 

 gasping for air. A small species of catfish (Schilbeodes) was killed 

 in large numbers, while the pickerel (Esox tridecimlineatus) was very 

 sluggish and swimming slowly at the surface. The following day 

 many pickerel were dead as well as some of the large perch. The 

 large sunfish (Eupomotis gibbosus) was not affected. Collections 

 of plankton samples at this time showed that the Anabaena had dis- 

 appeared although the water still remained somewhat turbid. The 

 third day fish were not noted at the surface. 



This treatment of the lake brings out the fact that although the 

 amount of copper sulphate used was considerably below the toxic 

 limits for the fish the biological conditions following the treatment 

 were so unfavorable that the fish died. The oxygen content of the 

 water generally drops following the killing of the algae, and in this 

 case the reduction was, for a short time, below a point at which the 

 fish could exist. Haine ('18) ascribes this oxygen reduction to the 

 bacterial oxidation of the dead algae and calls attention to the same 

 reduction in the amount of oxygen when algae in a body of water are 

 suddenly killed by some natural cause. The best known case of the 

 killing of fish by the sudden dying of algae is that reported by Bald- 

 win and Whipple ('06). 



These injurious after effects may be avoided by eradicating the 

 algae at the first indication of their development in quantity by several 

 treatments, instead of at the time of their maximal development ; in 



