Oklahoma.  Water temp 78.  Last Saturday my buddy and I went fishing at a local lake (Fort Gibson.)  We were fishing one of the bays near the dam in about 15' of water.  The night before we launched there was a violent rainstorm in the area, but we were now under blue skies with very little wind.  As we were moving up the bay toward where the feeder stream entered, we began to encounter huge masses of shad.  The lake was about 1/4 mile wide at this point.  Shad were roiling the surface as far as we could see in all directions.  There must have been tens of thousands of them.  I don't have much experience with shad behavior, but to me they acted like they were feeding on something.  There were very few panic-like jumps, so the bass didn't appear to be actively feeding on the shad.

Thinking we were on a bass gold mine we started fishing. We threw top-waters.  We dragged crank baits and spinner baits through them.  We threw deep divers under them and we even fished jigs. Not one bite.

My buddy and I have never experienced such a huge gathering of shad.  It was almost like being dropped into the middle of some SI-Fi movie.

If anyone has experienced this phenomenon, can you provide any explanation as to why this situation occurred?

Sounds like a shad spawn. I have caught many a bass casting small jerkbaits near these schools. The bass are likely still feeding on them, but not as obvious as when the shad try to avoid the predators. The shad have only one thing on their tiny little minds.

Happens every year here.

The bite literally sucks when there's that many baitfish.

You forget I was present during a mass sponge migration.

You forget I was present during a mass sponge migration.

From the same movie. Hmmmmmmm.

I have experienced the same thing. This is during the shad spawn. There is a small window when you can catch them. I had the most luck with a Rattle Trap type bait where you can change depth easily. After this window is closed the bite can be tough for at least two weeks. This happens on our cooling lakes here, when this happens forget these lakes for a while.

100% shad spawn. During this period it's best to find some smaller schools of shad away from the massive schools and fish around those. When you get shad bunched up like you're talking about, it's very difficult to get bit. If you go back, you might try a jigging spoon just below the shad.

The bass were probably full.  

wow, never seen that, though I have seen so many shad on the st. john's river that they beach themselves on lilly pads when trying to outrun predators.