A snake has eaten a crocodile in an epic duel that shocked onlookers at a Queensland lake.

The whopper snake took on the croc at Lake Moondarra, near Mount Isa, on Sunday, and the contest and its surprising result was captured on film.

Mount Isa mother Tiffany Corlis was having breakfast nearby when canoeists racing on the lake alerted her about the endurance battle playing out nearby.

She grabbed her camera and took a series of shots that documented the enormous snake's assault on the much smaller croc, which was about a metre long.

By the time Ms Corlis started watching, the snake had already coiled its body around the crocodile and was beginning to strangle it.

"(The crocodile) was fighting at the start, so it was trying to keep its head out of water and survive," she told ABC North West Queensland Radio on Monday.

"But as the morning sort of progressed, you could tell that both of them were getting a little weaker.

"Finally, the croc sort of gave in and the snake had uncoiled for a little while and had a brief break and then actually started to consume the crocodile."

Ms Corlis said it was amazing to witness.

"It was just unbelievable," she said. "We were sort of thinking that the snake had bitten off a little more than it could chew.

"But it did. It actually ate the crocodile."

The aftermath showed the overstuffed snake lying still, where presumably it stayed for some time as it digested its dinner.

"When you actually looked at the snake, you could actually see the crocodile's ridges, legs and everything inside its belly," Ms Corlis said.