Massachusetts State Police beefed up patrols around the reservoir that supplies Boston's drinking water after seven foreign students were caught trespassing in the area late at night.

With the city still jittery after the April 15 terror attack at the Boston Marathon, word that two women and five men, reportedly from Saudi Arabia, Pakistan and Singapore, had been found in the restricted area around the Quabbin Reservoir caused concerns. The reservoir serves Boston and some 40 other communities in the area.

“As an extra precaution, water quality samples were analyzed at MWRA’s lab yesterday and all came back normal," Ria Convery, of the Massachusetts Water Resources Authority, told the Boston Herald. “There is no evidence of any water quality issues at the Quabbin Reservoir following the trespassing incident.”

It was after midnight on Tuesday morning when a state trooper on patrol at the reservoir spotted two cars parked on the grass near one of Quabbin’s entrances. The cop investigated and found a group of seven people, five men and two women walking from the water back to their cars. When the police officer asked why they were trespassing, members of the group replied that they were chemical engineers and recent college graduates who had an educational interest in the reservoir, according to police.

The group was briefly held at the scene while background and warrant check were conducted but let go after their records turned up clean.

“There was no evidence that the seven were committing any crime beyond the trespassing,”  Massachusetts State police spokesman David Procopio told FoxNews.com, adding that officers on the scene checked the vehicles and the park area and did not locate any items out of place or of a criminal nature.

Procopio also said that a preliminary investigation determined the individuals were originally from Pakistan, Saudi Arabia, and Singapore. The Springfield field office of the FBI was contacted by the State Police and is assisting in an investigation.

“Further investigation is being undertaken because of the late hour when they were observed, their explanation for why they wanted to see the reservoir, and the fact that they were in an area marked no trespassing,” Procopio said.

Routine checks at numerous watersheds around the state have been stepped up as a precaution, but officials say nothing else has been reported as being out of the ordinary.

The seven individuals, whose identities were not released because of any formal arrest, will be summonsed to appear in a district court for trespassing. A court date is pending, according to officials.