This is where i got my information from when it came to flying over water:
Online shopping for a great selection of at the official DJI Online Store.
store.dji.com
*Beginner pilots should refrain from flying over water at any time.
Disable Vision Positioning System (VPS)
All DJI drones come equipped with VPS, a technology that maps the surface below to help position the drone. When flying over water, however, light reflecting off of the surface can cause issues with this technology. Because of this, it’s best to maintain a height of at least two meters above the water. If you have to fly below this height for a special shot, we recommend you turn off the VPS to avoid any unstable actions by the drone.
Caution: When you disable the VPS of your aircraft and the distance between water surface and drone is smaller than 2 meters, you should fly the drone with a low speed in your FOV (field of view). Also, the height needs to be adjusted frequently since the aircraft could possibly drift downwards. Be aware that the minimum height has to be above 1 meter when flying over water.