Bass Virus Spreading In Arizona Lakes

Game and Fish seeks help from boaters, fishermen to prevent spread of invasive species and fish diseases


Arizona Game and Fish Department officials have confirmed the presence of a largemouth bass virus in Lake Pleasant that also showed up in bass in Roosevelt Lake several years ago.

The discovery of the bass virus comes on top of several incidents this summer when a bloom of golden algae killed bass and other fish in Roosevelt Lake and the Salt River.

Lab tests on largemouth bass tissue samples collected during a routine survey in October by Arizona Game and Fish and U.S. Fish and Wildlife Service personnel showed presence of the disease in some samples. 

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

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

Game and Fish has not documented any fish kills at Lake Pleasant associated with largemouth bass virus to date. At this time, fishing is still very productive and there have been no recreational impacts. Lake Pleasant is the top fishing recreation site in Arizona, producing more than 520,000 angler use days.

Prior to this sampling, the only fish health survey that had been conducted at Lake Pleasant was in 2002, and largemouth bass virus was not detected then. Therefore, the virus most likely entered the Lake Pleasant fishery within the past 10 years.

Dahlberg explained that although the virus can cause mortality in largemouth bass, not all bass become infected, and not every fish becomes sick. For instance, only five lakes in Texas suffered fish kills even though the virus was found in 23 of the state’s reservoirs.

“Usually the number of infected fish that die is relatively low compared to the entire population, with the virus mostly affecting older and larger fish,” said Dahlberg.

The virus has been found in 18 states dating back to 1991. In Arizona, Saguaro Lake, Bartlett Lake, Roosevelt Lake, and now Lake Pleasant have tested positive for the disease. There have been no impacts attributable to largemouth bass virus at Saguaro, Bartlett or Roosevelt to date.


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