After two cliff diving deaths over the weekend, first responders from Thunder Bay are asking people to use common sense when diving into the unknown.

OPP Sergeant David Moscall said he'd like to see young people refrain from cliff diving, but there's nothing he can do to stop them.

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OPP boat used to recover body from Lake Superior at Silver Harbour Conservation Area on Monday. (CBC)

So it's up to the township and property owners to decide whether to post warnings on their land, he said. Without warning signs, there's no knowing what dangers lay below turbulent waters.

The lack of signs at popular cliff diving spots frustrates Shuniah Fire Chief Blair Arthur, who said fire and emergency service workers are called to the cliffs around the lake at least once a year to take injured jumpers from the water.

People don't realize how dangerous the water can be, Arthur added.

"Even if someone's got a twisted ankle, they are unable to get themselves out of a situation like that," he said. "So, there's still a chance of them dying from their injuries."

Arthur said warning signs would keep some jumpers off the cliffs, but noted the best deterrent is common sense.

Moscall echoed Arthur’s opinion.

"You never know what's under the water," he said.

"I guess that's part of the problem. It's a big lake and you can see that it's quite possible for an area that was safe yesterday to not possibly be safe today."