You have an underwater civilisation, be they merpeople, octopus people, partially evolved humans or not. One thing that is always considered as a necessity in the development of any society is mining.
The problem is that water deflects and slows down fast, slashing movements by friction. The deeper you are, the more the pressure and the less speed you could impart to your swing.
QUESTION: So how do you swing a pickaxe underwater with enough force to get to the desired ore?
How do you go about developing an underwater society who mine and use mining to evolve their society like man did on land?! Without starting right from the get go from a tech starting point and just say that they used a drill.
Even today, most mining is done by excavation wielding slightly improved 'pickaxes' and dynamite.
EDIT ~ For those interested. In my scenario I have partially adapted humans who have a Medieval, at best Renaissance era, level knowledge of how to mine on land (and under it). So I need to figure out how they would redevelop their techniques to underwater. They have protection from the water pressure and temperatures and an ability to breathe. They still have fully dexterous fingers (no webbing) ~