The BlurFix3 SO Naked 55mm Filter Adapter from Snake River allows you to mount 55mm underwater filters to your GoPro HERO3 action camera housing. Because water alters light at depth, tending to absorb red light, underwater filters are essential for ensuring proper white balance.
It is possible to use this adaptor with the GoPro HERO3+ action camera also, if you use the BacPac compatible housing, which is the same housing the HERO3 uses. Note that it will not attach to the standard housing that is included with the HERO3+.
Since the GoPro HERO3 and HERO3+ have optically ultra-wide lenses, slim or ultra low-profile filters are recommended for use with this adapter to avoid mechanical vignetting.