I've had to dodge a bird to two with my P2, but today I had to get out of the way of a low-flying aircraft. I don't think there was any real danger of us colliding; there was good separation for our relative speeds. But it was a bit unnerving. I was flying at a commercial fishing port/boat launch that also holds a farmers' market (like today) on occasion. Several weeks ago I asked for and received permission from the port director to fly. The site is about 20 miles from the closest airport. I wanted to get some photos and video of fishermen selling shrimp straight off their boats. At no time did I exceed 150 feet, and I was over water the entire time except for take-off and landing. It's Saturday. There's people buying shrimp off the boats. There's people under a 5,000 square foot, open-air shelter selling various goods. There's live music. And there's engine noise as people are launching their boats. Then I noticed a different engine noise coming from behind me. What I saw next was what looked like an American Champ flying over the launch and farmers' market at between 300 to 400 feet. It circled, flew off into the distance, came back and circled again at that same altitude, and then flew off again to be seen no more. As soon as I saw the plane, I dropped my altitude to below the height of the boats' trawl arms. I figured if the Champ collided with me, that would be the least of his worries because he would have already clipped one of the boats. But I thought manned aircraft, even small civilian aircraft, are supposed to maintain an altitude of no less than 1,000 feet as soon as they can climb to 1,000 feet. He was well below that altitude. He obviously was out for a weekend flight and wanted to do a fly-by of the farmers' market - maybe shooting some photos as he circled. I have no problem giving way to manned aircraft. And if had it been necessary, I would have cut power to my motors and fallen from the sky. But small plane pilots need to fly by the rules, too. Although there are idiots flying UAVs around Love Field and JFK, I would wager the first quadcopter/manned aircraft collision will be at an event like I was at today. It attracts UAV pilots who want some cool photos, as well as small plane pilots who want cool low-altitude photos and/or video. We'll both be sharing the same airspace and neither will be able to get out of the other's way.