In 2004, eight British servicemen were held in Iran after being seized in the Shatt al-Arab waterway, where they were training the Iraqi river patrol service.

BBC: Iranian navy detains five Britons on yacht in Gulf

The Coast Guard will patrol the river in boats with machine guns mounted on their bows.

CNN: Pope Benedict XVI begins first U.S. tour

The U.S. Coast Guard will deploy a Maritime Safety Security Team, akin to a seaborne SWAT team, as well as the 87-foot cutter Albacore to patrol the Potomac River.

CNN: Security at record high for WWII Memorial ceremony

Four security fences and a team of border patrol vehicles deter improvised river crossings.

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In all, 88 vehicles have been located, both in the river and amid the broken concrete wreckage of the bridge, according to the State Patrol.

NPR: Officials Warn of Possible Flaw in Nation's Bridges