By Alejandra Cancino
The FBI is asking dive shop owners to be on the lookout for suspicious behavior or criminal activity by their customers. The bureau recently issued a national advisory.
Judy Orihuela, a spokeswoman for the FBI's Miami office, said the routine advisories are sent out occasionally "just to give heads-up in things to look out for." 
Examples of what dive shops are asked to look out for include:
• Requests for special training that include diving in murky water or sewer pipes.
• Requests to learn advanced skills such as the use of re-breathers.
• Purchasing or renting Swimmer Delivery Vehicles and Diver Propulsion Vehicles.
• Paying in cash or refusing to provide personal information.
Re-breathers are normally used by the military because they make few or no bubbles and can allow people to stay in the water from three to eight hours; other systems allow people to stay in the water from 30 minutes to two hours. The time depends on the depth of the water.
People also use re-breathers when they want to photograph marine animals.
Alan Crooks, manager of Force E Scuba Centers in Riviera Beach, said regular customers don't dive in sewer pipes. South Florida Water Management District officials might send their own divers to check sewer pipes, he said, but he has never had a customer asking to dive in one.
Murky waters could include lakes, canals or rivers, and people generally dive in them when they live in landlocked states. In Florida, people don't usually dive in canals or lakes, but it's not a rare request.
A person who wants to scrub the bottom of a boat, for example, might want to learn to dive in a canal.
Crooks said his shop receives similar advisories twice a year. He said he knows most of his customers by name and hasn't reported anyone.
But if someone wanted training to dive in sewer pipes and was not affiliated with the South Florida Water Management District, Crooks said he would contact authorities.
"Every now and then, there are people who make you raise your eyebrow," he said. "But they are just people in general."
Original Source