I've hunted Black Moshannon a few times and here is what you can expect on opening day.
3/4 of the water is off limits to hunting, so close setups on both sides of you near road access is the norm.
More hunters than ducks on the lake, and 10 times more decoys set.
Hikers, bird watchers, kayaks, park rangers coming through all morning.
100yd shots by half the hunters. Steel shot raining down on you.
By 8-9am every duck in the lake as moved to a quieter|safer locale.
You can scratch out a Woodie or 2 during the circus and not get shot if your determined.
Do some extra scouting, nearby Beaver Ponds and streams that require some walking are better options.