ANGELS CAMP, Calif., May 17  Every May, they come. Thousands of slimy little athletes, primed for the biggest event of their careers, the World Series of competitive frog jumping: the Calaveras County Fair and Jumping Frog Jubilee.

Then, of course, it’s back to the pond.

But after nearly 80 years of peaceful jumping, a civil war of sorts has broken out among the human overseers of this annual, undeniably bizarre event, which was inspired by Mark Twain’s classic 1865 tall tale, “The Celebrated Jumping Frog of Calaveras County,” about an inveterate gambler and his gifted amphibian. The dispute, which pits the group that has long presided over the jump against the fair’s organizers, has resulted in a pair of dueling competitions this year, each planning to hold their finals on Sunday.

All of which has cast a pall over what should be the county’s biggest weekend of the year.

“It’s sad,” said Emily Stemler, 85, the director of the Angels Camp Museum and Carriage House, who attended the first competition in 1928. “I think they ought to get back together. But I guess you can’t stop what they call progress.”

The squabble has also divided many of the competitors, grown men and women who spend days and nights before the fair crawling around ponds and swamps looking for the perfect jumping frog. Known as frog jockeys, the handlers are clannish, working in teams of 10 or more to gather the frogs from waterlogged places around the state. Hundreds of human competitors, and more than 2,000 frogs, are expected to compete at the fair this weekend, with the top 50 advancing to the finals.