Scientific divers often work in remote areas, and sometimes far offshore.
In the photo below from author John Heine, research divers from Moss Landing Marine Laboratories instal light calibration sensors on a large optical buoy located 10 miles off the island of Lanai.
Special training is required to work in this blue water environment.
A detailed description of this, and many other types of scientific diving techniques, can be found in John's book on this subject, Scientific Diving Techniques: A Practical Guide for the Research Diver.