Hi Dave & others
Damariscotta Mills and the section of river that runs through Warren village are both good bets. At Damariscotta, you can get extremely close views of fish as they climb the fish ladder up into Damariscotta Lake.
At Warren, fish must pass through a large fish trap, where alewives are bailed and sold as lobster bait. This site (at Mill Park) also provides open sky views of diving ospreys and osprey/eagle sky battles. Fish are generally most abundant of the rising tides.
The traps is fully open during weekends to allow all fish free passage upriver. The bridge at Payson Park, on the west side of RTE 90, can offer some awesome flight shots of birds carrying fish. At Warren, mid-May thru mid-June is likely the high part of the
migration period.
Don