the phosphorus added to Lake Erie comes from 
municipal wastewater, and 66 per cent of the 
phosphorus is derived from detergents. Two-thirds 
of the phosphorous is retained in the lake, 
principally in its bottom sediments. Needless to 
say, the effects of municipal wastewater discharges 
have had a drastic effect on aging. There is no 
doubt that domestic sewage is a predominating 
contributor to the deterioration of water quality 
because of its nutrients, as well as its bacterial and 
organic contamination. 
2. Combined Storm Sewage 
Combined storm sewage sometimes is a greater 
problem than municipal wastewater. Combined 
storm sewage from a heavy rainfall can overtax the 
capacity of a treatment plant; hence, substantial 
volumes of untreated wastewater are bypassed to 
receiving bodies of water. 
3. Industrial Wastewater 
Often industrial wastes are routed to municipal 
treatment systems for the mutual benefit of the 
community and its industry. These wastes gener- 
ally have the effects discussed under Municipal 
Wastewater, paragraph 1 above. However, many 
large industries bordering the Great Lakes find it 
more economical to accomplish treatment within 
their own complex. Many do not effect a suitable 
degree of treatment, thus contributing to acceler- 
ated aging. Nutrient-laden effluents, organic con- 
taminants, noxious chemicals, and sediments or 
inorganic residues are contained in industrial 
wastewaters. 
4. Watercraft Wastes 
Wastes from watercraft are not treated to the 
extent of municipal wastewaters, or most often 
not at all. In the United States, recreational 
watercraft wastes are equivalent to that discharged 
by a community of 500,000. However, this contri- 
bution to water quality deterioration of the Great 
Lakes is insignificant by comparison with other 
nutrient sources. While its treatment is beneficial, 
especially to public health, it is very doubtful that 
watercraft wastes alone would accelerate aging of 
the Great Lakes. However, on a very local basis—at 
a marina, for example—it may cause very serious 
VI-124 
problems. Of course, the problem will grow as 
water transportation and recreational boating 
increase. 
5. Oil Discharges 
Oil discharges are undesirable, for they cause 
ecological inbalances and drastic effects on aes- 
thetics. On the other hand, special oils could 
have limited beneficial effects by reducing the 
penetration of the sunlight, necessary for the 
growth of algae that contribute to eutrophication. 
6. Dredging 
For many years harbors and channels in the 
Great Lakes have been dredged to provide suitable 
channels for waterborne transport. The spoil, rich 
in nutrients, usually consists of sediments carried 
by tributary streams and rivers and of sewage and 
industrial waste residues. Dumping spoil in the 
lakes, the practice for many years, releases more 
nutrients than when sediments and residues are 
undisturbed. Hence, dredging causes an increase in 
the recycling of sediment-stored nutrients, espe- 
cially phosphorous. Important benefits would 
accrue if the dredging spoil were deposited on 
isolated land so nutrients would not be washed 
again into the lakes. 
7. Thermal Discharges 
Thermal discharges can have both beneficial 
and detrimental effects on accelerated aging. Dis- 
charge of such heated effluents as industrial and 
power plant cooling water can induce extensive 
algal growth during seasons when water tempera- 
tures are normally too cold. Conversely, during 
seasons when water stagnates and becomes strati- 
fied in the Lakes, thermal discharges could help 
restore circulation. Stratification causes oxygen 
deficiencies in the bottom waters of a lake, in 
turn, causing vastly increased nutrient recycling 
from the bottom sediments. 
8. Nutrient-Laden Inflow from Tributaries 
Inflow from tributaries and impoundments add 
nutrients to the lakes. Because impoundments 
suffer the same aging problems, both the causes 
and remedies are essentially the same as for the 
lakes. This illustrates the need to treat the Great 
