black object in sky traveling above river, circle of light appearing to come from it lighting up river in just that area of light

On a hunting trip camping in a big football size field on the bank of the Molalla River - Dickie Prarie. Noticed a circle of light approx 20ft diam on the water, such as would appear coming from a helicopter search light. Traveling south to north. Appeared to be coming from a black spot in the sky approx 200ft in the air (no trees by the river in the area we were). As it travled the 3 of us looked up through our rifle scopes and could only see a black spot, but we could tell something was there as the stars were blacked out.   We watched the light on the river sweeping from side to side, move towards us, past us, until it was approx 300 ft. down river, then the light went off and we could not see any sign of anything at all. We heard no noise even when the light was shining on the river directly infront of our campsite. Another thing we noticed was at the time we heard no frogs, or other noises, just dead quiet other than the river flowing. About an hour later we noticed the frogs again started making their regular noises.  We only saw the circle of light on the river, and the black object (could not tell the size or shape just that the stars did not shine where it was) in the sky, we never saw a beam coming from the oject down to where the circular light was on the river.
Date is approximate.  PD