Filled out at mufon headquarters with witness on the phone by field investigator linda flechtner 18809 on august 17th, 2017. ---------------------------------------------------------------------- while on vacation, my family and i were fishing off the dock near the boat ramp on lake alvin in south dakota, near sioux falls. my daughter and son in law and the baby live near the area, i live in nebraska. it was about 10 pm, pitch black and the lake was calm. i saw a white spot light like light in the distance and asked "is that a tower light"? my son in law said no. the light was tree line high and kept coming towards us on the dock.It stopped over the lake. we could then see it was a large surf board shaped ship with four big white spot light like lights on it. it was dark and had a flat bottom. it was 45 to 65 feet long and 25 to 35 feet wide, and no deeper than 6 feet. it was about 4,000 yards from us and about 8oo yards high in the sky. the spot lights were about 3'6" large and every 90 degrees. it had two more lights in the center and little red lights in the back when it went over and away from us. as it came towards us on the dock, the engines seemed to come on and all hell broke loose. as it came closer it seemed to create a "vortex" the wind was whirling around us, the grass and the water. it had a ripple waves in the water under it, and when the fifth ripple came to the dock we heard the sound. it sounded like a sonic boom or lighting striking the ground. it was traveling real slow,but very loud and the air was swirling around us. after it flew directly over us and away, my daughter had been running to check on the infant and she felt as if she had been violated. an intense feeling. i asked if we were still in the present time and we were. alvin lake is not that big only about 115 acres. my daughter had said she'd seen a ufo at the lake on a previous occasion.