Couple theories, first water temp. I don't know what the river temp is, but the Bay is at 46F which is above where it normally is this time of the year. second is just me spit balling. Chesapeake's water supply comes from the plant upriver. The plant uses reverse osmosis to remove salt from the water. The byproduct is brine, which is discharged downstream. I don't know exactly where but I do remember a study at the time of construction that said the discharge would not affect water quality in the river. Questions.

1. What is the population growth in Chesapeake and hence the increased brine discharge since the plant was built?
2. Does it affect the fish's spawning run upstream, meaning can or do the fish sense the increased salinity and think they are going the wrong way and turn around?