Arizona Game and Fish Department officials have confirmed the presence of largemouth bass virus in Lake Pleasant after processing routine test samples obtained in October.

While the virus can affect largemouth bass, it doesn’t pose a risk to people or pets, and the water is safe for water supply and recreation.

“Largemouth bass virus is not known to infect any warm-blooded animals and any fish caught by anglers are safe to eat,” said Marc Dahlberg, AZGFD water quality program manager in a prepared statement. “However, we always recommend that people thoroughly cook any fish they intend to eat, and never use fish found dead or dying for food.”

To date, no fish kills associated with the virus have been documented by AZGFD. Fishing remains productive with no recreational impacts. Lake Pleasant is the top fishing recreation site in Arizona with at least 520,000 angler use days.

Prior to October’s sampling, fish surveys were conducted at Lake Pleasant in 2002. The virus most likely entered Lake Pleasant fishery within the past decade.

Although the virus can cause mortality among largemouth bass populations, not all bass become infected, and not every fish becomes sick. For example, five lakes in Texas suffered fish kills despite the virus being traced to 23 lakes in that state.

Historically, the virus has been detected in 18 stated since 1991. In Arizona, Saguaro Lake, Bartlett Lake, Roosevelt Lake, and now Lake Pleasant have tested positive for the disease.

Other fish species can carry the virus, too, but it only affects largemouth bass. Activation of disease outbreaks are unknown but have been known to be associated with stress events, such as high water temperatures. The virus diminishes overtime.

Precautions the public can take to help stop the spread of the disease — and other aquatic invasive species, such as quagga mussels — include not transporting live fish or water from one body of water to another.

“You might be spreading an unwanted disease or even introducing an unwanted organism, such as quagga mussels, that could substantially affect a fishery or lake ecosystem,” Dahlberg said in the statement, “Don’t transport live fish caught from a lake — period. It’s the wrong thing to do and it’s unlawful.”

Cleaning, draining and drying a watercraft before leaving any lake at any time is recommended, as is disinfecting the watercraft and waiting at least five days before launching it in another lake or body of water. The bass virus can survive up to a week in standing water.

Anyone who sees any dead or dying fish is asked to report observations to AZGFD 623-236-7257. For more information, visit

According to Bassmaster’s fact sheet, a largemouth bass with the virus may have trouble swimming, or remaining upright, because the disease attacks the swim bladder. Adult bass of two pounds and more seem to be the most susceptible to disease.

According to, largemouth bass are native to the St. Lawrence and Great Lakes, Hudson Bay, and the Mississippi River basin. The species was introduced in Arizona in 1897. Reports of largemouth bass weighing as much as 16 pounds have been caught. Largemouth bass are the second most popular fish in Arizona. The species is partial to habitats of submerged trees, aquatic vegetation and underwater drop-offs.

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