A water issue at Pimlico Race Course affected utilities at the facility, shutting down several sets of toilets on multiple floors and causing backups at those still in operation.
Kurt Kocher, a spokesman for the city's department of public works, said the problem was on Pimlico property.
Security was turning away increasingly frustrated event goers. Those already inside were being allowed re-entry due to the lack of facilities.
Track officials pointed to a water main break two miles from Old Hilltop, and said city crews were working to restore water.
Kocher rejected the notion that a break two miles away was responsible for the limited issues at the track.
Crews had dug up a portion of asphalt just behind the grandstands and city trucks were towing some cars to clear path.
Around 5:30 p.m., track staff announced that some water pressure had been restored to the grandstand but not all bathrooms were back online.