The Sennheiser MKE 2 GoPro underwater microphone will allow you to record audio with your GoPro underwater (though I’m not sure how many people want to do that). The microphone is completely waterproof up to 1m (3ft). Of course it can also be used as a regular external microphone on your GoPro.
The MKE 2 has a omni directional pick-up pattern and weighs in at 45g (0.1 lbs). The microphone also comes with a windjammer has been tested at speeds up to 60 MPH to help reduce any unwanted ambient noise. Unfortunately the MKE 2 is only compatible with the GoPro HERO 4 (silver and black), as well as the HERO 3+, but it won’t work with any of the HERO 5 line up.
The MKE 2 is available for $199.95US.
Here’s the untouched audio from the Sennheiser GoPro mic as we dunked it in water at their booth at NAB: