My cousin and I were fishing. Lake Minnewasta in Day County, SD on a small lake with very few cabins (5?, on the opposite side of the lake). We were on a sandbar surrounded by private farmland. We had our lines tangled and we were arguing about it. It was a clear night. We swear that the water got rougher after we had our encounter. This object came over our heads from the south and stayed right over us for some time. We could hold our arms out to explained how large it was, tell you that it had a humming sound and took off fast in almost straight up in a NW direction. It was big. The catch is that we could not see it, but it was there. We were so shaken we could hardly stand up. We have thought about hypnosis over the years to see if we could recall anything. We know that it was not man made techlogy and I have never heard anything like it since. I don't know if we were misiing time.