There is an emerging field of underwater forensics and investigation. It stretches from the more traditional underwater investigation of sunken ships, to the retrieval of bodies and evidence from lakes and rivers, to (most recently) the investigation of coral reefs. A series of workshops (called Coral Reef CSI) have been established to train marine biology invetigations (among a variety of other people) in techniques of crime scene investigation. The International Coral Reef Initiative (ICRI) has established a Committee on Coral Reef Enforcement in order to develop protocols for this practice.
What is interesting about this practice, in terms of underwater media, is that evidence can never really be seen in itself. It’s collected by divers who have to look through goggles, through water, with the help from an extensive technical apparatus. They can only stay underwater for an hour and often (in the case of reefs) have to be careful not to further damage the living object they are examining. In this way it parallels a medical examination.
In addition, water is a medium itself – sometimes it washes away critical pieces and at other times works to preserve the objects/bodies/incidents.
Also, FYI, 2008 is International Year of the Reef.