While fishing today I noticed large swarms of fish surfacing and breaking the water. At times, the swarm of fish could be as long as 8 foot wide. The water actually looked like it was boiling from all the action and swarming, just beneath the surface. The fish were often surfacing in the middle of the lake (it's a 7 acre lake). Out of curiousity I was able to quietly approach the swarm, and I noticed it was a group of bluegill, maybe 50 of them. I throw a redworm in the swarm (no weight, just hook-n-worm) and BAM, within one second a slab hit it. Instantly the fish disappeared, the water got calm, and the swarm was gone. After about ten minutes sitting there search for the swarm, they surfaced again, but now about 80' away! I turned the trolling motor on high, and approached them again. They were swarming and surfacing again, and once again I through my bait in the swarm and within seconds I had a bluegill on. (They were super aggressive!) Then, again, they disappeared, only to resurface minutes later several yards away. I chased the school around for a while in my boat until they stopped. They were all bluegill. I have NEVER seen bluegill do this before? What caused the fish to congregate and move around so quickly, (and I assume feed off of something on the surface). My buddy said they were all bulls. Some 'gills were on nests, but were very finicky, they would only bite if the worm was hanging in their face. Any ideas what this is?