Hello Everyone I am working on project which is under water application I am new I don't have deep knowledge about Bluetooth I am using Arduino BLE 33 in that board Ublox nina B306 5 Bluetooth is used in my application I want control the slave which is underwater and the master is remote which is in air so the my problem is when slave go into water it suddenly disconnect from master
could any buddy pls tell me what solution for my problem. Thank you and sorry about my English
No solution. You cannot break the laws of physics. Bluetooth uses a high frequency signal and high frequency radio waves cannot penetrate water more than a few millimeters.
There may be low frequency radio modules that would work somewhat better, but these are not Bluetooth and cannot be connected to your smartphone.
A cable ?
i want wireless communication
any other solution
Give information about the project as we do not know the conditions or limitations you need to address. We only know that your proposed solution doesn’t work
floating antenna wired to the underwater part...or floating BLE device connected to the underwater gig
Drop weighted coloured balls down to the ‘device’ and detect these and act on them depending on colour. Or different weights and a load sensor. Or a loud speaker and microphone
You can use Esp32/Esp8266 and control it from your phone
what do you mean ?
that won't work if the ESP is under water
It connects to the WiFi and it is in a sealed box
Or you can put the Esp on top of the water (making a sort of a cork and the wires to be underwater
WiFi is also at 2.4Ghz - it's a high frequency and thus won't work reliably if at all when in (even shallow) water
that was suggested in post #8
He can use the remote control and reciver from a mini submarine
He could teach a friendly dolphin to relay a message! 
yeah, I think the US Navy is selling used equipment on eBay... 
Toy Chinese submarines
There's a theme here.
You cannot use radio communication for the underwater part. It is simply not negotiable in any practical way as the military clearly knows (§). 
So you ask - what communication is used underwater?
The answer is - sonar.
This does not work so well in air, and particularly does not work through the water/ air interface. Similarly to the concept of using a buoy attached to the submarine part to implement a radio link to the above water "master", you would need a buoy with the sonar transceiver to communicate "wirelessly" with the submarine part.
Unless this is a serious project, I fear it is literally "dead in the water". 
(§: Very Low Frequency wireless communication is I believe used - in one direction - base to sub.)