Here is a drone capable of flying in the air and moving underwater. The Naviator, which was developed at Rutgers University, is ideal for search & rescue operations, inspection jobs, and other challenging tasks. The developers used two sets of propellers, for above and below water operations. When the drone is in the water, the upper propellers deactivate and lower propellers pull the drone underwater.
Once the drone is fully submerged, both sets of propellers work at a lower rate to extend battery life. More information is available here.