(CNN) An Australian couple has been rescued from a crocodile-ridden part of Australia's remote north after lighting a fire and scrawling the word "help" in mud to attract the attention of search crews.

Colen Nulgit, 20, and his girlfriend Shantelle Johnson, 18, went fishing on Sunday in Keep River National Park, in the Northern Territory near the border with Western Australia. There are saltwater crocodiles in all waterways around the park, according to the Northern Territory government

But Nulgit said their day of fishing turned into a freezing, sleepless overnight stay when their truck became "bogged" -- Australian slang for getting stuck in mud.

"Our hearts sank," Nulgit told CNN. "Just the feeling of getting bogged ... it's just pretty scary."

Nulgit said they had seen crocodile tracks in the area earlier and, as the waters rose and the sun set, became afraid of being swept away by a large tide -- or being attacked by crocodiles or dingos.

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