Federal agency emergency operations centers were not aware of or notified about the exercise, and they began implementing response procedures, a federal source said.
Flights at Washington's Reagan National Airport were grounded from 10:08 to 10:30 a.m. ET, said Diane Spitaliere of the Federal Aviation Administration.
Upon hearing media reports, the FBI dispatched agents who arrived at the water's edge before learning from other law enforcement agencies that it was an exercise, said Supervisory Special Agent Katherine Schweit, a spokeswoman for the FBI's Washington Field Office.
The police department's Harbor Patrol, which is responsible for patrolling the
Potomac, was not notified, law enforcement sources in Washington said.
The patrol has now demanded the Coast Guard notify it in the future before any training exercises on the Potomac, the sources said.