You see a water vortex.
It draws you nearer.
Location
Edron, Gray Island, below Outlaw Camp, east of Banuta, Factory Quarter (inaccessible).
Notes
If you just walk on it you are teleported to another place.
Looks the same as a Maelstrom and a Water Channel.
If you step in the one east of Banuta, you will receive the achievement Spectulation.