A kick here, a shove there. Bodies crash together in turns. And watch out for those stinging jellyfish!

Just another day of open water swimming, where athletes challenge waves, wind and each other in rough-and-tumble conditions that might shock Michael Phelps, Grant Hackett and the rest of the pool crowd.

"It's a wrestling match in the water," said American Mark Warkentin, competing in his first world championships.

"Just about anything goes, short of grabbing people," teammate Scott Kaufman adds.

Well, that happens, too.

American Chloe Sutton, who at 15 is one of the youngest competitors, told her coaches after Sunday's 5-kilometer race that other swimmers were hurting her.

"Well, hurt them back," she was instructed.

"I don't want to do that," she replied. "Then they'll retaliate to my retaliation."

Clearly it helps packing a killer instinct along with your goggles for what can be roller derby in the water.

Open water swimming makes its Olympic debut next year in Beijing with a 10-kilometer race.

"It does extend that dream to some other people that don't have that shot in the pool," said Kaufman, who will compete in Wednesday's 10k. "The Olympics is what we're all shooting for."

The world championships are staged every year at distances of 5, 10 and 25 kilometers. Swimmers have to complete a certain number of loops around the course depending on the event's distance.

Each turn is manned by a judge, and boats carrying technical officials and medical personnel roam the water. Swimmers can be disqualified for pacing, slipstreaming, walking, jumping or finishing without their transponders.

Like soccer, the first time swimmers infringe on competitors they are shown a yellow flag and a card bearing their number. A second offense brings a red flag and an ejection.

"The only rule is you're not supposed to impede somebody's progress," Kaufman said. "Who really knows what that means? The people on the boats can only see a certain amount of the physical stuff. They probably can't see anything underwater."

Larisa Ilchenko of Russia, who won her fourth consecutive 5K world title Sunday, accused American Leah Gingrich of hitting her in the eye when Gingrich allegedly used a breaststroke kick.

"I actually got dragged underwater by someone as well at one stage, but that sort of stuff just happens," said Gingrich, who is 17 and competing in her first major senior-level international meet.

Some of the Americans turned to open water after finding meager success in pool swimming.

"In the pool, I'm not very good," said Sutton, the 10K Pan Pacific gold medalist who will swim in Tuesday's 10K women's race. "I don't make finals at our nationals. I just love swimming in the ocean. It's so exciting and so beautiful."

Fear can be a factor, too.

Thousands of jellyfish invaded the course in Port Phillip Bay off famed St. Kilda beach for last Sunday's 5K race. Sutton got stung on her elbow and compared it to brushing against a cactus.

Teammate Kalyn Keller, the 10K silver medalist at last year's Pan Pacific Championships, cringed at the prospect of creepy, crawly sea creatures chomping on her.

"Not being able to see everything under the water is a little frightening," she said. "I still get a little freaked out. I think that's why I swim fast. I just want to get out. It's swimming out of fear."

The uncontrolled chaos reaches its peak around turns, with swimmers jockeying to clear the buoys. And all that scrapping makes swimmers hungry and tired.

Coaches on pontoon boats are allowed to deliver power bars and cups of juice or water using long sticks. With a carefully timed roll, the swimmers swipe the treats, toss them into their mouths and continue.

"You have to try to find the cup that your team has," Sutton said. "People are purposely knocking all the cups down."

Swimmers stash gel packs loaded with carbohydrates and a dash of flavoring in their suits, pulling them out to suck on as needed. Sutton wrinkled her face in describing the taste, adding, "When your mouth is full of salt water, you can't really taste anything."