From the depths of Lake Nicaragua comes a fish story to rival "The Old Man and the Sea" and the legend of Moby Dick.
Lake residents - everyone from wizened old fishermen to housewives who wash clothes on the shore - insist that deep down in these murky brown waters are man-eating sharks."You used to see a dozen an hour," said Mariano Roblero, who operates a tour boat from the lake port city of Granada. "You could see their fins. Sometimes they would even upset the boats."
Unlike most fishing lore, such accounts actually check out. For years, scientists have maintained that Lake Nicaragua is the only freshwater lake in the world with sharks.
The evidence dates back to 1526 when the Spanish explorer Gonzalo Fernandez de Oviedo wrote of Nicaragua's freshwater sharks. They also impressed E.G. Squire, the first U.S envoy to Nicaragua.
"Sharks abound in the lake. They are called `Tigrones' for their rapacity. . . . Instances are known of their having attacked and killed bathers within a stone's throw of the beach at Granada," Squire wrote in 1852.
At first, experts explained the phenomenon by saying Lake Nicaragua used to form part of the Pacific Ocean and became land locked through a series of volcanic eruptions. Sharks and other marine life, they said, adapted as the water lost its salt content.
But after a decade of research, including an extensive tagging program, American zoologist Thomas B. Thorson determined that bull sharks in search of food make their way into the lake through the San Juan River, which connects Lake Nicaragua with the Atlantic Ocean.
While no fully freshwater sharks are known, the bull shark is a ferocious and versatile predator capable of functioning either in fresh or salt water, Thorson wrote in a 1966 study titled "The Status of the Freshwater Shark in Lake Nicaragua."