I have flown my P4 over many different types of water from large rivers, 1 mile wide, to small rivers, small streams,waterfalls, rapids, etc. Never had a problem until the last 2 flights. The last flight was over a small creek with flowing water and some faster water over rapids. Trees lined both banks with a small clear area between them. Water was muddy, a light brown color and shadows under the trees with bright spots with glare away from the trees. It was a bright sunny day. I started the flight by flying about 20 feet from the bank and 10 feet over the water where there was fast water over very small rapids. It would not hover and moved in the direction of the water flow. I had complete control of it and decided to fly upstream. I flew upstream a fair distance until trees on both banks blocked my way. My speed was very slow, 1 to 2 mph before stopping under a tree with a dark shadow where the water was flowing but not rapids. My P4 went up several feet and began to go backwards in the direction of the water. I started to turn and go forwards just as my props hit some leaves. I thought sure I was going in the water but I was able to fly away and return home safely. That was my blessing for the day!! When I got back to the car, I decided to test the P4 from the parking lot. It hovered rock solid. I think these conditions were just right to fool the sensors. My P4 has been rock solid over land and water except for these last flights. I also calibrated the IMU before the last flight.