This shocking footage shows the moment two light aircraft swooped so low over an estuary that they were almost "skimming the water".
The two pilots were spotted soaring along a sea wall at the River Blackwater, near Maldon, Essex - a mere eight feet above the water's surface.
The privately-owned light aircraft, which appear to be based at Popham Airfield in Basingstoke, Hants., swooped so low and close to the sea wall that it appeared as if one of them was going to land on it.
And a shocked birdwatcher who was standing near the water last Tuesday (Dec 15) said he was left wondering whether he would need to jump out of the way of the two planes.
The man in his 50s, who did not wish to be named, said: "The plane in front was practically skimming the surface of the water as it came in.
"It was probably only about eight feet above the river as it passed me. I was quite shocked. He was flying extremely low.
"You can't even fly a drone that low, usually.
"There's a lot of birds and wildlife in that area - all it would have taken was one mallard duck or a migrating goose taking off from the water in front of the plane, and he would have been in trouble."
The man added: "He was originally coming down towards the sea wall, and it looked like he was going to land on it - but then he carried on along the estuary.
"The shock wasn't even how close he was to me - it was that he was potentially putting himself at risk.
"It's not every day that you go birdwatching and see aircraft just a few metres away from you."
It is not clear what the two aircraft were doing in the area.
And the man said: "I don't know whether they were authorised to be there, or whether there was something wrong with the aircraft and they couldn't gain height.
"I don't know the circumstances. But I don't think I've ever seen any footage before of private aircraft flying so low as these two."
The Civil Aviation Authority has been contacted for comment.