Ive kayaked the river 6 times and was always successful either pass shooting ducks flying between the trees on the sloughs or setting up in shallow flats or ponds with a handful of decoys when the tide comes in. You can get setup with a kayak, travel rack, and blind / cover for under $1k and have access to spots holding birds every day of the season.
Its worth remembering that ducks like to hide, just because you dont see a cyclone of them from the road doesnt mean they arent there.