ALGAE IN WATER SUPPLIES 93 



blue green, which stains the pebbles, sticks, etc., over which it is smeared. The appearance 

 of this scum is sometimes spoken of as the working of the lakes, from the resemblance 

 to the collection of scum on cider, etc., when fermenting, or, as an idiom expresses it, 

 "working." The odor given off by this putrefaction can be detected from some distance. 

 In speaking of the water bloom, Prof. Dwight C. Marsh says : 

 This phenomenon is especially marked in Lake Winnebago in some summers. It is 

 due, of course, to the enormous growth of the plants of the plankton, that growth being 

 particularly fostered by the hot weather of midsummer. The plants especially concerned 

 in forming the bloom are Clathrocystis, Anabaena, Aphanwomenonfi Oscillaria, Lyngbya, and 

 Cloiotrichia. .The times of occurrence of these plants have already been noticed in the dis- 

 cussion of the individual constituents of the plankton. At the middle of August, in some 

 summers, on a still day, the surface of Lake Winnebago is apparently a solid, opaque green. 

 Some of this material decomposes, and as the currents slowly move along the surface 

 material, it shows a wavy streaked appearance like the surface of polished malachite. Its 

 intrinsic beauty, however, does not attract the average person, for he looks upon it as 

 "scum," and he thinks of it simply as an evidence of filth. This material is thrown upon 

 the shores by the waves until the rocks alongshore are completely covered with it, and it" 

 may in its decay become very offensive. Following the maximum period of the "bloom," 

 Cladoplwra appears and covers the littoral rocks with a thick mat of green. This great 

 growth of "bloom" naturally attracts the attention of the non-scientific observer, and many 

 absurd explanations of its appearance are given. The most common one in Oshkosh is that 

 it is a mass of seeds coming from the marshy shore of the Fox and Wolf above Ohkosh. 

 Doubtless the Anabaena and Cloiotrichia have given rise to the supposition that the bloom is 

 a mass of seeds. The decomposition of Cloiotrichia produces a blood red coloring matter 

 which is sometimes very noticeable on the shores of l,ake Winnebago, and has led people to 

 question as to whether the lake is not affected by one of the plagues of F^ypt. 



When the water is still the plants of the bloom are in greatest abundance, close to 

 the surface, ' and are distributed very uniformly over the lake. Frequently, in the latter 

 part of July and in August, there may be seen floating about yellowish green masses of a 

 more or less spherical outline, perhaps as much as three inches or more in diameter. These 

 masses, which are composed of aggregations of Aphanizomenon mingled with scattered fronds 

 of Cloiotrichia and Anabaena^ have very little coherence and elude the collector by falling 

 in pieces almost at a touch. As is evident from the discussion of the occurrence of the 

 algal constituents of the plankton, the bloom is not a prominent feature of the deep lakes, — 

 in fact, in some years the growth of these algae is hardly noticed by the ordinary observer, — 

 and of the shallow lakes few seem to produce as large an amount as is seen in Lake 

 Winnebago. Of the lakes under observation, Shawano and Pelican were the only ones that 

 could be compared at all with Lake Winnebago. 



Odors produced by the decomposition of organic matter in water are easily 

 detected. Sometimes they are grassy and sometimes mouldy or musty. Some- 

 times the odor is decidedly fishy, which is especially true of some of the higher 

 plants like Myriophyllum or Potamogeton. Mr. Whipple* says that the cucum- 

 ber taste found in the Boston water supplies was due to a fresh water sponge. 

 He made a series of experiments with oil of peppermint and other oils and he 

 found that the oil of peppermint could be recognized when the dilution was 

 1 to 50,000,000; oil of cloves, 1 to 8,000,000; cod liver oil, 1 in 8,000,000. 

 Kerosene oil could not be detected when diluted to 1 in 8,000. Accord- 

 ing to Whipple, aromatic odors are produced by certain diatoms ; grassy odors 

 are produced by certain blue-green algae like Anabaena and Rivularia; the 

 sweet grassy odor is produced by Clathrocystis; Volvox produces a fishy odor, 

 while Pandorina and Eudorina produce a faintly fishy odor. Certain protozoa 

 produce fishy and oily odors. 



Perhaps the most extensive investigation of microscopical organisms in 

 water are those reported by the Massachusetts State Board of Health. Special 

 methods for determining the amount of impurities found in water are given 

 in these reports. Prof. Parker has shown that when the odors are pronounced 

 the organisms are always present in considerable numbers. He says : 



