By Adam Harrington

Illinois (WBBM) -- A potentially dangerous phosphorus flare was found at Montrose Beach this week, and the U.S. Coast Guard said three more remain unaccounted for.

Coast Guard Sector Lake Michigan said the flares were used for a joint military exercise with the Air Force earlier this month offshore from Milwaukee. Four phosphorus pyrotechnics failed to activate when they hit the water during the exercise, the Coast Guard said.

The flares are considered armed if they do not activate. When they do, they produce a red smoke and flame that can reach 2,900 degrees Fahrenheit, the Coast Guard said.

The flares ignite when they hit water, after a cap and screw are removed.

One flare was found on Monday by a lifeguard at Montrose Beach — a popular beach known in particular for its dog-friendly area and its piping plovers. The newest generation of birds laid their first egg at the beach just last week.

Chicago beaches also opened for the season this week.

The Coast Guard said three live phosphorus pyrotechnics from the exercise in Milwaukee are still out there. Anyone who finds a silver-colored cylinder on the beach should call 911, the Coast Guard said.

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