American swimmer Michael Phelps, the most decorated Olympian of all time, was arrested for drunken driving early on Tuesday after speeding and then crossing the double-lane lines inside a Baltimore tunnel, police said, according to The Associated Press.

The 18-time Olympic gold medalist later apologized for the incident, saying he was "deeply sorry to everyone I have let down," the AP reported.

"Earlier this morning, I was arrested and charged with DUI (driving under the influence), excessive speeding and crossing double lane lines," Phelps said, according to the AP. "I understand the severity of my actions and take full responsibility," he added. "I know these words may not mean much right now but I am deeply sorry to everyone I have let down."

Police said Phelps, 29, was clocked by radar around 1:40 a.m. traveling 84 miles per hour in a 45-mph zone and was booked and released, according to the AP.

Phelps, who has won 22 Olympic medals and appears to be eyeing a spot on the U.S. team for the 2016 Olympics, was "unable to perform satisfactorily a series of standard field sobriety tests," authorities said, adding that he'd previously failed a Breathalyzer test, the AP reported.

Police said an officer followed Phelps' 2014 Land Rover onto northbound Interstate 95, through the Fort McHenry Tunnel under Baltimore Harbor, and pulled him over just beyond the tunnel's toll plaza, according to the AP. Authorities said the Baltimore-area native was cooperative.

The drunken-driving arrest was the second for Phelps, who has spent most his life working feverishly in the pool, but admits he likes to have a good time outside of practice and competition, the AP reported.

Emerging recently from a two-year retirement, Phelps first tested the comeback waters in April at a low-key meet in Phoenix and his progress has been steady rather than his usual impressive, according to the AP.