Dear jifigz,
If you looked at the article I posted in this thread it does a good job of describing several of the water issues. They are not necessarily pollution issues but in the lower Susquehanna there are thermal issues that occur with run-off during storms at critical times. Unusual heat followed by torrential rain leads to elevated water temperatures in the shallow shoreline water that is detrimental to the spawn. It would be nice if Mike the fish guy chimed in, but I think that development along the river has increased the probability of thermal problems during critical times of the year where water temperature plays a large part in fish patterns and behavior. It makes sense to me that there could be issues when eggs are laid on schedule in 59-degree water and then 80 plus degree four-lane highway and parking lot run-off washes over the beds a few days later. But what do I know? 😉
Regards,
Tim Murphy 🙂