I got my first experience of completely flat "water" / "oily" water, flying low over a completely deserted and very cold freshwater reservoir in wintertime. CFI is with me, and a second aircraft is playing chase plane while we've been shooting video with on a short cross country... Loose formation flying, spins with the chase plane standing off and ahead a ways to try to capture the timing right for good shots of a spin entry, etc. The "chase" plane and our airplane both had ham radio gear aboard for air-to-air, patched into our respective intercom systems, and separate PTT. Two of us in one Skyhawk, three in the other. All hams. We're headed home, puttering along about 50' above the absolutely flat surface of this frozen reservoir with somehow almost no snow on it yet, so depth perception is quite "challenging". Chase aircraft is on our port side, 150' higher, taking video. Isn't a soul for miles, it's just ridiculously cold out, but clear and "crisp" as they say... From the FM ham gear I hear... Chase pilot: "How low are you guys?" I'm flying and the CFI is keeping me honest on not losing a single inch more altitude, so he replies, "Pretty low." "What are you guys using for depth perception there, the small chunks of ice in the water?" "I don't know what Nathan's using, but I'm using the fish." I had to pop up another 25' I was laughing so hard.