Testing done on water samples from the Quabbin Reservoir showed no abnormalities after seven people were seen at a reservoir park entrance shortly after midnight, officials said Wednesday.

The Massachusetts Water Resources Authority said water quality samples were analyzed at its lab Tuesday and all came back normal after the alleged trespassing incident.

The central Massachusetts reservoir supplies drinking water to Boston.

State police spokesman David Procopio said a trooper saw two cars parked at a reservoir park entrance at 12:30 a.m. Tuesday, then saw five young men and two young women walking toward them from the reservoir. Procopio said Tuesday that the men told police they recently graduated from chemical engineering programs and were curious about the reservoir.

Procopio said they are from Pakistan, Saudi Arabia and Singapore with addresses in Amherst, Cambridge, Sunderland and Northampton, and New York City. He said law enforcement databases show no warrants, detainers or advisories on them.

In a statement Wednesday, the authority said it uses a 24-hour "state-of-the-art, real-time monitoring system" that detects abnormalities immediately. The water is tested daily for its biological, chemical and physical properties.

As an extra precaution, water quality samples were analyzed at the authority's lab after the incident.

"As is our protocol, when anything unusual occurs, we conducted additional testing for a wider range of potential contaminants in more locations," the Water Resources Authority said in its statement.

"There is no evidence of any water quality issues at the Quabbin Reservoir following the trespassing incident," the authority said.

State police did not release the names of the seven people. Procopio said they will face trespassing charges at a later date.

Greg Comcowich, a spokesman for the Boston FBI, said the FBI was notified about the incident, which he said is routine when "critical infrastructure" such as water supplies or electrical systems are involved. He would not comment on the incident.