Tried for an adventurous shot today. Visited the local fish quay. Flew tello out over the side.
Almost immediately i got 'visual posituoning not available' and it started to drift back, away from me.
(Luckily it wasnt out into the river)
It probably depends on the visible field of view of the downwards camera. And as I remember the documentation states that bodies of water are not a great idea to fly over
Good thing nothing happend to your tello.
I also have flown the Tello over water! Once the drone lost positioning, drifted quickly down wind and ... out of range. When I reacquired the signal, I could not see the drone...so I increased altitude and looked around until I could tell with first person view how to return. It is easy to lose sight of the drone, especially when using a range extender.
The second time I flew over water, I was less than 20 feet and Tello went into auto land mode! The Tello got with in a couple of feet of landing on the water before I coached her back up into the air...i have video of that!
I will attest that flying over water is hazardous to the future of your tello. I still do it, but try to stay very close to an edge or other objects, (boats) in the water.
Nice and calm today so tried a second shot. Had a friend with me as a spotter to keep an eye on things, as it's easy to lose your bearings when watching the screen and the position of the drone.
Had a little backwards drift (with the direction of the wind) but vertical height was steady. Could have possibly gone further 'out' into the river but don't want to push my luck
Tried to fly over a small canal first and then a lake yesterday. Like other people already wrote in this thread it loses its ability to position itself based on downward cameras and goes into autoland mode and/or drifts in some random direction. When I was over a canal this random direction was trees but at least the canal is narrow and as soon as it reaches the edge it stabilizes again. But then I tried over a lake (from my kayak and btw I own a DJI Mavic Air that also uses downward cameras but has zero problems flying above water) and the thing started rushing away like before and when I finally regained control it went into auto-land. I kept trying to override its autoland and it kept fighting me all the time. Same thing was the drift away, I kept trying to fly it back to my kayak and it kept drifting away. When I would push full throttle + full tilt in my direction to override its autoland and return to me it would just hover and if I let go of controls it would quickly drift away and then start to land. Scary because I could not make it return. I was lucky my gf was with me on my kayak, so while I was pushing full throttle to fight the autoland and full tilt in my direction to fight the drift away she paddled under the dumm little Tello and then I grabbed it with my hands, got a cut, lost a prop which bounced of my finger, but at least I (we) saved it.
The home button is on my (paid) app TelloFpv only.
Word of caution: Return to Home uses VPS data. VPS does not work over water.
The reason why a Mavic Air has no problem over water is that VPS is only one more sensor (use for precision hover over land). If it fails like over water the Mavic Air just uses GPS and IMU only (resulting in a less stable hover but no significant drift)