I haven't looked at this thread in ages but for some reason clicked on your post. This would be quite the notable event if it actually occurred. Prior to the ditchings, if the aircraft were ever 1,000 ft AGL or so, ATC flight-following RADAR (or whatever they call it now) would probably have primary echo recordings of the aircraft even if no transponders were turned on. This would help establish the tracks and terminal locations. Once in the reservoir, it should not take long to locate the aircraft using SONAR or other methods if they are there.
I wonder if these aircraft were actually ultralights, whether spraying or not, and landed normally somewhere near the reservoir.
I will try to learn more.
I forgot to add that the children were evacuated and removed to the old remaining "bomb shelter" in Gettysburg under the old Junior high. This tells me that TPTB were NOT aware of any legitimate sprayings and were concerned....