Hi, today we sadly saw our Phantom 4 drift down to the bottom of a river and we weren't able to rescue it. The drone was flying at 75 feet of altitude and at around 100 feet away from us. All of the sudden we got the Weak Signal and within 2 seconds we got the Aircraft Disconnected message. We ran closer to gain reception and pressed the Return Back Home and we saw the drone just fall to the bottom of the river. The weird thing is that with over 18 hours of flight, we had never encountered this situation before. We had all of the latest firmware up to date, fully charged controller battery, fully charged iPad Mini battery and fully charged Phantom 4 smart battery. Now we have no way to rescue the drone and it is lost forever. I wonder how many people has this happened to. It almost feels as if there was an electrical cut-out or power off which caused the drone to just loose connection with the controller. As we review the video reference recorded on the iPad, the video just cuts off as if the entire P4 just shut off on mid air. How can I report to DJI? We have the flight report available.