Unidentified Black Sphere

While fishing, my grandfather and I noticed a dark shaped oval object appear above pine trees.  It was the size of a bus.  It made no sound.  The tree tops beneath it swayed in all directions.  It was a clear moon lit night.  My grandfather said "do you see that? "  I said "yup".   He then noticed the hands on his watch were spinning.  We both looked at each other.   As he said, "its time to get the hell out of here!"  He started up the out board motor and we headed back to camp.
Over 20 years later, my dad and I returned to the same lake to find it a dead lake.  No life in it at all.   It was teaming with baitfish, gamefish, panfish and wildlife 20 plus years ago.
Witness indicates that date is approximate.  PD