Flounder feeding????

[getonfish]

So yesterday while fishing I came across a group of flounder that were going crazy on a school of shad. I pulled up on them and started casting away but nothing. I threw the whole tackle box at them for 20 minutes and not one single hit even with Gulp. I would not think to much of this except that this is the second time. The same thing happened earlier this month with a school of small trout feeding on shad. I have noticed that the amount of bait in the lake is tremendous but the bite is slower (at least for me) this year than it was last year. Is it possibly the fact that there is so much bait that the feeding schedule is fast and short?