Eight people were discovered hiding in a storm drain near St. Paul's Watergate Marina on Tuesday morning, after what authorities said was a dangerous excursion into an underground shaft bored into the river bluff.

Police said public works workers saw the group of young people on the bluff near Shepard Road about 10:15 a.m. and called police. After police arrived, they called for a technical rescue team from the fire department.

Firefighters used ropes and ladders to get into the underground passageway to see if anyone had gone inside. Assistant fire chief Mike Gaede said the young people didn't initially respond to searchers, and appeared to be trying to avoid detection.

Police said they'd taken all eight into custody. Six were juveniles from 15 to 17 years old. Two 18 year olds were also taken into custody. One was taken to the hospital for an unrelated medical condition. The other was arrested for gross misdemeanor trespassing on a public utility. The six juveniles were being held for release to their parents.

"I cannot stress how dangerous this is," said St. Paul police spokesman Mike Ernster. "It's dangerous for people to be entering these bluffs for the simple fact that you don't know what's in there, and the situations can change dramatically in a storm drain. You don't know what could be coming down that drain or what's in there."

It's the second time in a little more than a week rescuers have had to enter St. Paul's labyrinth of caves and utility tunnels. Firefighters had to rescue two teenagers from a cave on the city's West Side just before Thanksgiving.