A US state confirmed for the first time a virus that affects fish after the death of 220 specimens in one of its lakes

The California Department of Fish and Wildlife confirmed the presence of Largemouth Bass Virus following the death of two hundred twenty fish at Lake of the Pines. (Illustrative image Infobae)California confirmed the presence of Largemouth Bass Virus (LMBV) in its territory for the first time, following a fish die-off recorded in September at Lake of the Pines, a private lake in Nevada County. The finding adds a new concern for freshwater species conservation and for recreational fishing, due to the difficulty of controlling the disease once it becomes established in a fish population. The California Department of Fish and Wildlife (CDFW) announced the detection on November 12, 2026, after analyzing largemouth bass and bluegill specimens. Tests confirmed the presence of the pathogen, while authorities began assessments to determine whether it is also circulating in other bodies of water in the state. Although the virus can cause significant losses in fish populations, it poses no danger to humans or to other warm-blooded animals. The state agency asked anglers and visitors to avoid moving fish, bait, water, and contaminated equipment between lakes to reduce the chances of spread. The episode occurred at Lake of the Pines, a private lake of 232 acres (about 94 hectares), located in Nevada County, in northern California. During September, the death of approximately 220 fish was recorded, mostly largemouth bass, although bluegill specimens, also known as bluegill sunfish, were also counted. After receiving information about the die-off, the CDFW sent samples to the Fish Health Laboratory, where necropsies were performed that allowed confirmation of infection by Largemouth Bass Virus. The investigation determined that the pathogen was present in the fish examined, but did not establish how it entered the lake. The agency identified possible routes of introduction: contaminated equipment, infected bait, stocking of carrier bass, and the introduction of species capable of carrying the virus. However, none of these possibilities was confirmed as the origin of the episode. The CDFW also did not identify a specific activity as responsible for the pathogen's arrival at Lake of the Pines. The detection constitutes the first official confirmation of the virus in California. The authority continues to evaluate other aquatic environments to determine whether there are more affected populations. The necropsies performed by the Fish Health Laboratory identified the pathogen, although authorities still do not know the exact origin of the infection in the lake. (Illustrative image Infobae)Largemouth Bass Virus poses no risk to human health. The CDFW clarified that people can eat infected bass, swim in waters where the pathogen is present, and even drink that water without any health hazard directly associated with the disease. The same consideration applies to other warm-blooded animals, such as dogs, birds, and wild mammals. The virus is associated with certain fish species and is not considered a threat to people or to those animals. The recommendation to cook fish properly relates to the prevention of other foodborne illnesses and not to a specific danger associated with LMBV. The authorities' main concern focuses on fish populations and on the consequences the infection may have for aquatic ecosystems and recreational fishing. Jay Rowan, chief of the CDFW Fisheries Branch, noted that the finding raises alarm because of the widespread distribution of largemouth bass in California, its popularity among sport anglers, and its economic importance to rural communities. For that reason, the agency requested the cooperation of residents and visitors to prevent the pathogen from reaching other lakes and reservoirs. LMBV was first documented in Florida during the 1990s and subsequently spread to various regions of the United States. Its confirmation in California expands its geographic presence within the country and represents the first known detection of the pathogen in this state. The disease primarily affects largemouth bass, but it can also cause clinical signs in other species, such as smallmouth bass. In contrast, some fish, including bluegill, spotted bass, and crappie, can carry and transmit the virus without showing visible symptoms. This difference complicates prevention efforts, because an apparently healthy fish can contribute to moving the pathogen from one aquatic environment to another. Among the mechanisms that can favor its spread are:Infected fish: the movement of live or dead specimens can introduce the virus into other bodies of water. Contaminated bait: fish used as bait can carry the pathogen. Fishing equipment: gear that comes into contact with contaminated water or mud can contribute to its spread. Boats: water accumulated in tanks, livewells, and compartments can move organisms between different lakes. Introduction of carrier species: some fish can carry the virus without showing evident signs of infection. Once the pathogen becomes established in a largemouth bass population, it is extremely difficult to eradicate. There are currently no vaccines or treatments available to prevent or stop outbreaks. The virus poses no health risk to people who eat fish or swim in the water, nor does it affect warm-blooded mammals. (Illustrative image Infobae)Infected fish may show various physical and behavioral changes. Among the signs identified by the CDFW are sores or ulcers on the skin, darkening of coloration, swelling of the body cavity, bulging eyes, and redness. They may also exhibit lethargy, uncoordinated movements, and difficulty diving. Some fish remain near the surface or swim erratically, behaviors that can signal a health problem. The CDFW explained that certain factors can trigger the disease in fish that already carry the pathogen. These include elevated water temperatures during summer, poor quality of the aquatic environment, and stress associated with fishing. These conditions can increase stress in infected fish and promote the appearance of symptoms, but they do not prove that they caused the die-off recorded at Lake of the Pines. Outbreaks can last for several days or weeks before subsiding on their own. One of their most significant consequences is the mortality of a high percentage of the largest largemouth bass. Fish that survive can develop resistance over time, allowing populations to begin recovering. However, the loss of large specimens can affect a population for several years, due to the time these size classes need to recover. Given the first confirmed detection, the CDFW asked anglers and users of recreational water areas to adopt preventive measures at all lakes and reservoirs. The recommendation is to assume that the virus could be present in any body of water and to avoid actions that facilitate its transfer. One of the main instructions is not to transport live or dead fish or parts of these specimens away from the location where they were caught, except when they are intended for immediate consumption. If fish are cleaned, the remains should be placed in the trash and not discarded into other aquatic environments. The agency also asked that leftover bait be disposed of in trash receptacles, rather than released into the water or moved to another fishing spot. Boats should leave the area without accumulated water in their compartments. This instruction covers bait tanks, bilges, livewells, and the lines used to wash equipment or tackle. Another measure is to clean and dry any gear that has been in contact with water or mud. The agency recommended rinsing equipment, washing it with hot water, and allowing it to dry completely before using it at another lake. The CDFW also asked that fish to be returned to the water be handled carefully, because stress can increase mortality in infected fish. While the evaluation of other bodies of water in California continues, authorities asked that any significant die-off of largemouth bass be reported to the agency's regional offices. The goal is to identify possible new outbreak sites and reduce opportunities for spread to other fish populations.