I've heard various references about how flying over / close to the water can cause the Phantom 4 to drop

Can someone elaborate on this?   I'm interested in shooting some video along a deserted beach as close to the ground as possible, and / or as close to the water as possible.

If you check out the last 30 seconds of my video at : , you can kinda see where I'm trying to get too.

Does obstacle avoidance only work on forward motion?   What do they define as foward in terms of things like the ground?   Will it cause the Phantom to raise elevation? By how much, etc

Any hints, tricks, tips, etc would be greatly appreciated.

Nice video image quality. About your question i supose the water absorves the signal from the ultrasonic sensors or avoid those sensors from calculate the altitude. In solid ground the ultrasonic sensors works ok.  I think DJI advice a minimum altitude to fly safety (Any way Best to check the manual to be sure).   Obstacle avoidance only works wen obstacles are in front of the obstacles sensors  ( Front of the Drone) Range  2 - 49 feet (0.7 - 15 m).
Thats why in Following mode you must to be aware if " flying back" is enable cause if thers an obstacle the drone dont see it. Sensors are just in front of the drone.

It's a nice video.The obstacle sensing system can only detect the things in front of the drone.
And here is a safety tip of using the VPS system:

Great info!!

Does GPS take priority over the VPS?