have relatively high mercury levels. Eels, in turn, are fed upon by eagles, 

 directly or indirectly (eels serve as prey for common mergansers, which are 

 eaten by eagles). Recent mercury levels in bald eagle eggs are among the 

 highest ever recorded. Mercury contamination results in thinning of eggshells 

 and embryo mortality. 



Thermal pollution . Heated waters, when discharged into the environment, 

 raise the temperature of the receiving water. The extent to which the 

 temperature is raised depends upon the amount of heated discharge, the amount 

 of diluting water available, and the mixing rate. Heated discharge may come 

 from sources such as nuclear power generation, oil power generation, heavy 

 machine operations, industrial operations, and even fish hatchery operations. 

 The magnitude of the thermal impacts depends on the location and frequency of 

 activity. Cold water may be discharged from large, deep impoundments. 



Industrial point sources, including power generation, are the largest 

 contributors of thermal pollution in the coastal zone. Approximately 1 

 billion gallons of thermally treated water enter the characterization area 

 every day. Montsweag Bay in region 2 receives 85%, while Penobscot Bay in 

 region 4 and South Portland Harbor in region 1 receive 11% and 4%, 

 respectively (table 3-6). 



Thermally treated water affects the physiological functions and behavior of 

 certain aquatic organisms (e.g., phytoplankton, benthic invertebrates, and 



Table 3-6. Major Thermal Discharges in the Characterization Area from 

 Combined Industrial and Municipal Point Sources 3 . 



Region Amount % of Receiving water body 



(millions total and temperature range 



gal/day) 



1 47 4 S. Portland Harbor 100° to 210°F 



2 927 85 Montsweag Bay 116° to 180°F 



3 <1 <1 Medomak River 84° to 85°F 



4 118 11 Penobscot River 60° to 120°F 



5 



6 <1 <1 E. Machias River 97°F 



Total 1092 100 



a Maine Department of Environmental Protection files 



3-30 



