I believe this happened in 1987. I was living in Schevenigen (spelling) in the Netherlands. The city was sponsoring an international air show. The Red Arrows put on a fantastic display and as they were heading back to the UK a Fokker 100 (factory test bird) came in and was flying about 50 feet over the surface of the North Sea. His wake vortex stirred up a lot of water long after he disappeared heading back the Schipol Airport.