Lake Anna has had a reputation as a hot fishing lake since 1974, two years after it was created as a coolant for a Vepco nuclear power plant. Thermal enrichment is the term scientists use to explain the beneficial effect on life forms in the lake. Fishermen just know the striped bass and largemouth bass grow big and hungry.

But now comes a controversial report that says all the life supported by Lake Anna's warm water is not friendly. A Virginia researcher who studied the lake for three years says he found concentrations of an organism there that can cause a potentially fatal nervous system disorder.

Dr. Richard Duma, an expert on infectious diseases at the Medical College of Virginia, says the organism--called naegleria--which can enter the body through the victim's nose, thrives in fresh water heated above 85 degrees fahrenheit. He found the organism in nine lakes he studied in the state, with the highest concentration in Anna. He recommended that lake be closed to swimming when the water temperature exceeded 85 degrees.

Spokesmen for the utility company, which owns the lake water; the state of Virginia, which owns the land under it, and merchants who make their living servicing people who use it for recreation, dispute the findings of the study, which was published last year but only became controversial last week.

Vepco spokesman Rodney Smith said the utility company had not posted warning signs around the lake or informed local government officials of the study because talks with state health officials convinced them the danger involved is very minute.

"There is a risk, but a very, very remote risk in the opinion of experts," said Dr. Robert Stroube, an official with Virginia's health protection and environmental management department, who says he discussed the report with public health officials in Florida, where the organism is more commonly found. "We did not feel any kind of warning signs were needed. Drowning is a greater risk."

Joe Boggs, who owns a marina and food store on the 13,000-acre lake 80 miles southwest of Washington, says the report has generated "a lot of vicious rumors." Many of Boggs' customers come to the lake to swim and water ski. And that group, he says, has been most concerned by the sensational reports.

"This has slowed the business down," said Boggs, who spent much of last week answering phone calls from customers and friends. "It scares people."

Duma became interested in the warm-water organism when he encountered some cases of primary amoebic meningoencephalitis in the late 1960s. The patients had been swimming in lakes in Virginia's Chesterfield County. Working with federal funds and the Environmental Protection Agency, Duma became the foremost authority on the disease in the state. Looking back 50 years through state records, Duma found 17 cases of fatalities that he believes were caused by the naegleria organism.

None of those cases involved Lake Anna. But in the 10 years since the lake was formed by damming what had been a lazy stream of water known as the North Anna River, it has been the subject of controversy.

Environmentalists were opposed to the lake because of the ecological changes it would cause. Opponents of nuclear energy took the power plant to court on the argument that it sat on an unstable geological fault.

In 1978, a University of Virginia scientist claimed that fish in the lake were contaminated by Kepone and mercury. But a later study concluded that there was no evidence of harmful contamination.

"Somebody always wants to get their names in the headlines," said Boggs last week. "Your chances of being struck by lightning are much greater than getting that disease."

Boggs is one merchant who actively shows his confidence in the quality of the water. He swims and scuba dives in Lake Anna and says when his throat gets dry while diving, he has been known to take a few sips of the water.

"I wonder," said Boggs mischievously, "if the fishermen weren't trying to scare the water skiers off."