Prosser Reservoir near Truckee, California, and some are lighter than air!
This activity has an interesting history. If I remember correctly, the first known fish to be caught from a hot air balloon was in 2001. For several years after that, there was actually a hot air balloon fishing derby held here (I caught this photo in 2006). You can imagine that not all aeronauts (balloon pilots) are expert fishermen, so there were probably enough fishing lures caught in the balloons that they decided not to encourage the new sport. I'm sure the balloons are made from a very durable rip-stop fabric, but still, it's probably not a great idea to be poking new holes in a balloon which has to carry a basket full of people hundreds to thousands of feet off the ground.
I don't think they hold the hot air fishing derby any more, but there are probably still a few folks who attempt the interesting feat of catching a fish from a hot air balloon. You know that someone's keeping track of who has caught the biggest fish so far, and others will be trying to beat it.