new MFT Camera

For underwater, an inexpensive camera such as an olympus E-PL1, with an appropriate lens and underwater housing should do a great job.

As a replacement for your Nikon I would suggest the Panasonic GH3 or Olympus E-M5.

It really depends on a few factors:

- What lenes do you plan to use? If using primes, Olympus might be a better choice. If you want stabilized zooms then Panasonic might be better.

- What video quality is acceptable to you?

- What size and weight are acceptable?

- Which camera feels better to you? Test the ergonomics in a camera store if you can.

- Are you happy with a detachable or no viewfinder? If so, then a GX1, E-PL5 or E-PM2 might be a great choice.