This question is somewhat open ended and subjective… there really isn’t a good answer to this question. From a general standpoint, ever since the introduction of the GoPro and related Action Sports cameras at an affordable value (under $500) there has been a huge increase in consumers (non professionals) taking photos underwater.
My last trip to Hawaii I had a wild experience at Hanauma Bay. It felt like every where I went there was another tourist with a little GoPro strapped to their wrist. It was by far the camera of choice.
Now the early versions of the GoPro were still ground breaking, but low in pixel quality and video resolution. It was not until the HD Hero version came out in late 2010 that introduced full HD video (along with 5MP photos – same as the 2008 Digital Hero 5 model. In late 2011 the photo quality was bumped up to 11MP with the HD Hero 2. GoPro Data from Wikipedia: GoPro
Now oddly enough – if you checkout Google Trends, there has actually been a decline in the search term “Underwater Photography” in Blue and “Underwater Camera” from 2004 until now.
Now let’s see what happens when we add the search term GoPro into that mix. The term GoPro is represented in yellow.
So – When did Underwater Photography become popular?
Well – in general the searches around Underwater Photography were on the decline from 2005-2010. Then around 2010 when the GoPro HD Hero was introduced we see GoPro taking over “underwater Camera” and “Underwater Photography” in the search ranks. by 2011 when the HD Hero 2 was introduced, GoPro interest took off and basically started to replace searches on underwater topics.