Metro restored normal Yellow Line service after three hours of afternoon single-tracking due to a water leak in a tunnel, the transit agency said.
Water spraying into the Yellow Line tunnel south of the L'Enfant Plaza station prompted Metro to power down the third rail for a portion of the track.
The structure of the tunnel wasn't at risk, Metro said, but they didn't want water to spray on the electrified rail.
Metro single-tracked between L'Enfant Plaza and Pentagon City from about 11:30 a.m. to 2:30 p.m. while repairing the leak.
Metro said it has not determined whether ground water or water from a pipe outside the Metro system breached the tunnel.