Lakes as a total basin, implementing preventive 
and restorative measures for tributaries as well as 
the lakes themselves. (This aspect is discussed 
further below.) 
9. Waterfowl 
The Great Lakes, on an extensively used migra- 
tory flyway, are a resting and habitat area for large 
numbers of waterfowl. However, the birds’ contri- 
bution to eutrophication of the Lakes is a part of 
the natural aging process. 
10. Fisheries 
That fisheries have suffered from water quality 
deterioration in the Great Lakes is well known. 
Actually, the annual catch of all species in Lake 
Erie has not decreased with accelerated eutrophi- 
cation. However, less desirable species have 
supplanted the more desirable game fish, because 
spawning and rearing areas have been contami- 
nated or destroyed. The bottom fauna have been 
changed by pollutants and sediments, altering the 
game fish food supply so only the more tolerant, 
less desirable species can thrive. 
The predation of sea lamprey has had some 
impact, but this has been less important recently 
in Lake Erie than in Lakes Michigan and Superior. 
The purposeful addition of nutrients is a 
common technique for increasing fish production 
in lakes, while catching or removing large quanti- 
ties of fish constitutes a reduction of nutrients. 
This is important in the Great Lakes because 
planning and management of fisheries resources 
can benefit nutrient control. For example, nutri- 
ent removal as part of a restoration program 
requires that dead alewives which wash ashore 
from Lake Michigan be removed. Additionally, 
alewives can be a source of protein. Hence, two 
functions can be accomplished concurrently: 
nutrient removal by vigorous fishing for an unde- 
sirable species and production of a significant 
amount of protein. 
11. Sediment Interchange 
Sedimentation (including silt, erosion and agri- 
cultural runoff, dead biological life, and waste- 
water residues) constitute the second most 
important source of nutrients in the Great Lakes. 
As silt and erosion runoff flow into the lake, 
nutrients are dissolved and are available for bio- 
logical utilization. Land use practices, especially 
land development in urban and agricultural areas, 
have contributed to accelerated aging; measures 
must be undertaken to control this nutrient 
source. 
12. Agricultural Runoff 
Agricultural runoff, another very important 
source of nutrients entering the Great Lakes, 
consists of eroded soil, leached salts and fertilizers, 
and excess fertilizer. Measures to alleviate some of 
the nutrient contribution in the runoff include 
contour plowing and other land management 
techniques, judicious fertilizer application, and 
control of agricultural wastewater where possible. 
It is difficult to control nutrients in agricultural 
runoff, because treatment methods cannot be 
applied to point sources. It is a problem of, 
perhaps, the same magnitude as combined storm 
sewage. In the Midwest alone, it is estimated that 
the nutrients from animal wastes are equivalent to 
that from 300 million people. Obviously, only a 
fraction reaches the Great Lakes, but the potential 
from this source is enormous. 
13. Urban Land Drainage 
Although distinguished from combined storm 
sewage, this problem has many similar elements, 
assuming that a separate sewer system exists for 
storm runoff. Urban or storm drainage is com- 
posed of such nutrient materials as street sedi- 
ments, grit, oils, salts, and street refuse. It usually 
is discharged directly to a receiving body of water, 
because the potential contamination by pathogens 
is quite low; yet, the nutrient concentration may 
not be low, particularly in rich soil areas. 
14. Subsurface Waste Disposal 
Rural areas and many development areas 
around the Great Lakes have septic fields for 
domestic wastewater disposal. Nutrients in sub- 
stantial amounts drain to the lakes in areas having 
certain soil characteristics; however, these regions 
are fairly dispersed and do not constitute a major 
source of nutrients. 
VI-125 
