A young father is desperately searching for his $40,000 prosthetic leg after it fell into the ocean while he was jet skiing.

Toby Bird, from Newcastle in New South Wales, was crossing Lake Macquarie with a friend on Monday when he hit a wave and immediately sensed something was wrong.

The 24-year-old looked down and saw his right leg had come off. He believes he lost it near Pelican around 3 p.m.

“I looked down and thought, ‘Oh man, my leg fell off,'” Mr Bird told the Newcastle Herald.

Toby Bird, 24, lost his artificial leg while jet skiing on Monday. Photo: Facebook/Toby Bird

The young father spent $40,000 on the limb used for water sports. Photo: GoFundMe

“We stopped and went back to look for him, but he had just disappeared.”

The fitness instructor said he thought the unsecured leg could have sunk below the surface of the water.

“I have another one for getting around, but this one is for when I jet ski and swim,” he said.

Local divers offered to help Mr Bird but returned empty-handed after one dive.

Mr Bird lost his leg in a car accident in 2013. Photo: Facebook/Toby Bird

He asked on Facebook for anyone who spotted the leg in the water to contact him. Photo: Facebook/Toby Bird

Mr Bird lost his leg in a car accident five years ago after he swerved to avoid pedestrians and crashed straight into a pole.

On Monday, Mr Bird’s friend Shane Selby launched a GoFundMe page to raise the $40,000 needed to replace a prosthesis if the missing one cannot be located.

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