Maybe they were putting on some show or something. Thinking they're dolphins
Hahaha, fat, ugly, stinky ass dolphins...
Awww you guys are so mean!
Heh, yeah carp jump for a variety of reasons. I've seen some carp come all the way out of the water, and let me tell you watching a 20+ pound fish, jump and the subsequent splash that follows is interesting. I've actually had to double take a few times while at very public places because I thought a small child just fell in, lol.
The reasons are varied and we probably will never understand. Supposedly, like Bam stated, they do so to clean debris and/or parasites like leeches out of their gill areas. It could also be water quality reasons that cause them to jump, much like fish in a home tank will jump from the tank onto the floor if the PH balances get screwed. In the spring you will see a lot of "jumping/swirling" at the edges for spawning...
Frankly though after watching them on the banks now, I swear they jump just to see what is going on. Like one jumps, looks about..goes back down and says,
"Hey guys, it is that fool with the rods again, dun eat the corn!"