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Almost all of the natural lakes of Iowa develop at certain periods throughout the summer and fall months, heavy growths of small floating plant life commonly known as blue-green algae. These tiny, primitive organisms develop rapidly in certain lakes, and often form unsightly, paint-like scums over calm lake surfaces, and particularly along lee shores. Upon decomposition of these heavy scums, or "bloom" as they are commonly termed, terrifically foul, pig-pen odors issue therefrom, making human living conditions in the vicinity intolerable, and limiting to a large degree all aquatic recreation. In addition to these unwholesome attributes, certain species of blue-green algae occasionally develop poisonous substances that cause almost instant death to birds and mammals that drink water containing these plants. Present evidence indicates that the healthy, living plants are the most poisonous to warm blooded animals. Upon decomposition of large masses of algae, fish are sometimes killed in great numbers as observed by Prescott (1931), and Mackenthum, Herman and Bartsch (1948). Heavy losses of fish have been observed in Iowa on several occasions where heavy blooms caused diurnal declines of dissolved oxygen, and the algae were not toxic at the time. Our data indicates that only a few species of algae may become toxic, in fact clinical data points to but one, Anabaena flos-aquae, although certainly there may be others equally poisonous at times. A very comprehensive summary of the literature by Olson (1951), includes many authentic references showing that toxic algae may include many species and are of world-wide distribution. His clinical and field observations of the effects of toxic algae in the Minnesota lakes closely parallel those of the Iowa waters.

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Proceedings of the Iowa Academy of Science





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©1953 Iowa Academy of Science, Inc.



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