number of special stations were established in 1930. The data from these 

 special stations is discussed in the four folloiidng sections. 



Extent of pollution out from the mouth of 

 River Raisin 



Table 92 shows the data obtained at ten stations located on 

 a line from the mouth of the river to Station 13U, at a distance of 11 

 miles. The table is self-explanatory, and mention need be made of only 

 a few of the less obvious points and the conclusions to be drawn from 

 the data. The deposits at Station 200 were similar to those found at 

 the mouth of Maumee in 1929, but contained more sand, and organic 

 debris of a woody nature, and less sludge-like material and oil. The 

 odors were less putrid also. The number of Tubificidae at Stations 200 

 and 211 indicate a change from heavy pollution to moderate pollution 

 within a half mile of the river's mouth. Judging by the single sample 

 at Station 210, the dividing line should come between Stations 210 and 

 211, At Station 213, one-half mile farther out in the lake, the number 

 of Tubificidae indicate clean bottom, but at Station 117, one mile out 

 from Station 213, there was a reversion to light pollution. 



Thus the station tvjo miles from the river was polluted more 

 than the station one mile from the river, a situation not unusual in 

 this general area, or near the mouth of Detroit River, The explanation 

 is probably to be found in the shifting about of the organic debris. 

 Another possible factor is that of the unevenness of the bottom. The 

 shifting organic debris would tend to collect in depressions of the 

 bottom, though these were only slightly lower than the surrounding area. 

 Thus, if Station 213 were located on relatively high ground, it might show 

 less pollution than a station farther from the river, but located in a 

 slight depression. 



At Station 26h, two miles out from Station 117, the tubificid 

 count in the single sample was low. In view of the very light pollution 

 at Station 117 in 1930, and the absence of pollution in 1929> it is not 

 unreasonable to suppose that the single sample is representative of the 

 bottom in the vicinity of Station 261;, at least to the extent of in- 

 dicating the absence of pollution. At Station 263 and farther out the 

 evidence for clean bottom is conclusive. 



28U 



