With all the bird/fish kills happening at so many different locations around the world, I would doubt it would be caused by a single nuclear plant in the US. The bird/fish kill in Arkansas basically was one type of bird and one type of fish (I believe), so I would also think that if it was from some sort of release from the plant it would cause similar cases in other types of birds/fish not to mention animals/humans but of course I am just guessing.
I know that when I was stationed in North Carolina we had 2 or 3 fish kills in 4 years, I believe they were mullet but was put out that it was do to poor oxygen levels. Maybe these things just naturally occur.