Why do fish jump?

I've seen fish jump out of the water in a lake and it wasn't immediately obvious to me why it would be necessary.  Maybe some of them like the air, like some people like water?  Maybe they just like to jump for fun?  Regardless, I was interested in seeing if there was an actual reason why a fish might decide to jump.

From reading around it seemed like there wasn't an exact consensus but there were a few things that seemed to be repeated.  One reason is that some fish feed on insects that are at or hovering near the surface of the water, so they'll jump out to eat them.  Or the fish might be trying to escape a predator and hope to throw them off by leaving the water temporarily.  Since air is much less dense than water a fish can move much quicker through it.  Some think it could be an attempt to remove parasites, though others think it's unlikely.

The size of the body of water doesn't seem to matter.  Fish may jump out of the ocean or even garden ponds.  One explanation for the garden pond was high ammonia levels causing burns on the fish!  The one somewhat unique (and rambley) explanation was that fish just jump for the fun of it.  I've jumped or ran around for fun so even though it may not be the only reason fish jump, it at least seems plausible.