CHICAGO (CBS) — Six people were rescued Monday night from a boat that first took on water, then capsized miles out into Lake Michigan.

Around 9 p.m., first responders received reports of a vessel taking in water 2 1/2 miles offshore from Navy Pier, according to Jason Lach, Deputy District Fire Chief in Charge of Marine Dive Operations.

Police and fire crews went on a search mission to find the boat. Police found the boat first and rescued four people, and fire crews rescued two more, Lach said.

No one was injured, but everyone was taken to Northwestern Memorial Hospital for monitoring, officials said.

At the first report, the reports were that the boat was sinking. But by the time police and fire crews arrived, the boat had capsized, Lach said.

The boat was a 25-foot power boat, he said. It was not clear why it had been taking on water or why it capsized and was upside-down, he said.

It was believed to be a group of friends on the private boat, rather than a charter, Lach said. Everyone was wearing life jackets, he said.

“The water level is extremely high, so everybody – boaters as well as swimmers that go out there – really need to pay attention; realize how much higher, how much bigger the waves can be at this time of the year, as well as the water temperature’s cooling off right now – it’s about 62 degrees – so hypothermia can set in rather quickly,” Lach said.