East Hampton Village police arrested five Ross Upper School students on the evening of June 18 at the East Hampton Nature Trail, charging all five with possession of open containers of alcohol. One of the students, four of whom are foreign nationals, was charged with possession of marijuana. Because the five are all 17 or younger, police did not release their names.Police were tipped off to the youths’ nightly activities by a video posted on Facebook. According to the man who posted it, Dell Cullum, the five were part of a larger group that has been congregating for the past year in the 23-acre preserve between David’s and Huntting Lanes.They would pull up benches, he said, and leave them facing each other on the ground between two streams. They left empty beer cans, cigarette butts, and other rubbish not only around the benches but in the water, which is home to ducks and other creatures.Mr. Cullum, who every morning has been cleaning up the mess left behind the night before, said things really began getting out of hand about three months ago.“It was disgusting,” he said. He decided to shoot the video after a particularly bad morning. “It looked like somebody backed up with a pickup truck full of garbage and threw it in the water.” A few days after the video was posted it came to the attention of the police.According to Chief Gerard Larsen, as well as the police reports, two officers on bicycles were sent into the park about 7:30 p.m., one entering the preserve from David’s Lane, the other from Huntting. The first officer to come upon them said there were 11 youths present. In his report, he wrote that he “came upon a group of individuals drinking beer and a strong odor of marijuana in the air.” The teens “fled on foot” toward Huntting Lane, where the second officer was able to detain five of them.Handcuffed, the five were led down a path, out of the park, into the back of police cars, and on to police headquarters. They were issued appearance tickets for future arraignment in East Hampton Town Justice Court and were eventually released to Ross School officials.Patty Lein, the head of the Ross Upper School, did not return a call requesting comment.