We're not taking throwing a body tied to a rock into the river. Authorities are concerned that terrorists may resort to planting bombs by scuba diving:
"The FBI is asking the nation's scuba instructors to watch for potential terrorist threats.
The agency's Joint Terrorism Task Force recently alerted dive shops around the country to look out for divers seeking advanced training, including diving in murky water and in sewer pipes.
The advisory asked instructors to be aware of "odd inquiries that are inconsistent with recreational diving." That includes advanced navigation techniques, deep diving and the use of underwater vehicles."
The advisory also referred to requests for diver training "by applicants from countries where diving is not a common recreational activity" and training sponsored by religious organizations, cults, charities and other groups not usually associated with diving."
Having dived up around Hood Canal up by Puget Sound in Washington, I can understand why officials would be worried about underwater bombs. Being underwater is totally a hidden endeavor. No one can see you and a few well placed bombs could cause a lot of damage to ports and military installations along our coasts.
It's also a way to enter the country without being noticed. All one would need is a ride up relatively close to shore and the rest is a piece of cake especially if it's dark.
It's also a good way for terrorists to take pictures and gather information regarding target areas without being seen. If they can fly planes, they can learn to dive. Both can result in destruction.
Point: It's easy to get away with scuba terrorism because unlike the skies which can be patroled, underwater is virtually unguarded territory.