This is a very open ended question. The British Sub Aquatic Club1 publishes an annual incident report covering accident in their area. This is an excellent report if the question is about the dangers...
Some scuba diving places are Hathaway's Pond in Massachusetts, the Atlantic Ocean, and other places. In the US, you can scuba dive anywhere where the public is allowed to swim, except pools.
Most profitable one is to own a dive shop and training center. Taking 10 students on OPEN WATER at £300 a go makes you some decent money. add to that the income from gear sales, and other training...