As you can see below most of the salmon tributaries drain into Lake Iliamna.
The Pebble mine might be 100 miles from nowhere but in Alaska that's no all that far, especially considering the salmon rivers in that district would be sterilized should a breach happen in the mine's retaining pond - no matter how well designed.
Here is the map of the fishing districts in BB:
Which side of the discussion one is on seems to boil down to a handful of mining jobs verses an established industry ... do you side with jobs and income for a small number of people for a relatively short period of time, or with a sustainable fishery which has employed and fed people worldwide for over a century; do you prefer salmon from fish farms filled with the goodness of antibiotics, food dye, cuprous oxide and other delicious additives, or do you prefer your salmon as nature created it?