A virus in the Great Lakes region of the U.S. threatens 19 species of fish, including muskellunge, walleye and small-mouthed bass, and may harm New York state's $2 billion-a-year sports-fishing economy.

An infection called viral hemorrhagic septicemia, which causes anemia and severe bleeding, has led to the death of hundreds of thousands of fish in the state this year, according to a statement released today by Cornell University scientists in Ithaca, New York. The virus doesn't hurt humans and isn't associated with salmon or trout.

The New York State Department of Environmental Conservation, in Albany, has issued guidelines for sport fishers and boaters, aimed at curbing the virus. The infection may lead to less fishing. The pastime contributed an estimated $2 billion to the state's economy in 2003, the latest year for which a figure is available, according to the American Sportfishing Association, based in Alexandria, Virginia.

''We don't know the direct impact on recreational resources, but there is the potential this could be significant,'' said Paul Bowser, a Cornell professor of aquatic animal medicine, in a telephone interview. ''There needs to be a heightened awareness of the virus. Individuals will need to contribute to the big effort to prevent its spread.''

While Bowser was speaking of New York, other states are also affected. The sport-fishing economy in 2005 totaled an estimated $2.4 billion in Wisconsin, $2.8 billion in Minnesota, $1.6 billion in Indiana, $2 billion in Ohio and $1.6 billion in Pennsylvania, according to the association.

Rapid Deaths

Viral hemorrhagic septicemia, or VHS, causes bleeding, unusual behavior, and ''the rapid onset of death,'' according to the Web site of the New York State Department of Environmental Conservation. Other fish illnesses cause the same symptoms, the Web site said, so it is difficult to tell what is making the fish sick. In addition, not all infected fish show signs of the ailment.

Wisconsin, Minnesota, Indiana, Ohio, Pennsylvania and New York all allow commercial fishing as well. The sales from commercial fishing in the Great Lakes totaled $13.5 million in 2005, according to the Great Lakes Science Center, an Ann Arbor, Michigan division of the U.S. Geological Survey, a federal agency. Among the commercial fish affected are catfish and walleye.

Though the disease was known in Europe 50 years ago, Bowser said, this variation of the virus probably came from Atlantic Ocean-dwelling fish. It is unclear how freshwater fish became infected, he said. Nor is it clear how many animals will ultimately be infected.

'Worst Case'

Tens of thousands of drum were found dead on the shores of Lake Erie in the spring of 2006, Bowser said.

''The worst-case scenario is the 2006 Erie incident,'' he said. ''So many fish died that the bodies piled up on the shore, 10 feet wide and four feet high.''

The state conservation department issued guidelines for people using the water recreationally to prevent the spread of the disease. Fish shouldn't be transported from one body of water to another; to do so is illegal without a permit. Bait fish should only be used in the body of water they were taken from. Commercial bait shouldn't be used in any body of water. Fish carcasses shouldn't be disposed of in water. Any boats that are sailed in an infected body of water should be cleaned.

New York's guidelines were released in March as a temporary measure, and the department is reviewing public comments to determine if they ought to be adopted permanently, said Maureen Wren, a spokeswoman for the department.

Infected Waters

''Our regulations on fish movement are stringent, but they're ultimately for the protection of the economy that relies on a healthy and strong fishery,'' she said in a telephone interview today.

Infected bodies of water include Lake Huron, Lake St. Clair, Lake Erie, Lake Ontario, the St. Lawrence River, Conesus Lake, and the Niagara River, Bowser said. There was a presumptive finding of the virus in Lake Winnebago, which drains into Green Bay; confirmation is needed.

The Paris-based Organization for Animal Health, the animal equivalent of the World Health Association, requires that infections be confirmed by the U.S. Department of Agriculture's Animal and Plant Health Inspection Service.

If the virus is confirmed, the Organization for Animal Health must be notified. The organization has classified VHS as a disease with profound economic consequences, so it must be reported to the international community immediately when discovered.