Not forgeting bacterial and parasitic diseases, water quality issues, predation and poaching the biggest threat to carp and carp fisheries is that of viral diseases which continue to spread around the country.
Carp Edema Virus (CEV) Also known as koi sleepy disease (KSD). The latest emerging carp only viral disease "CEV is now considered to be one of the most important viral pathogens of carp". First identified in fisheries the UK in 2012 and kept relatively un-reported in this sector there have actually been more than ten confirmed fishery outbreaks since then including a significant mortality at Walthamstow in the Greater London area in 2017 and two in Ireland in 2018. Worringly it has been seen to cause mortalities in the UK at all temperatures down to as low as 3c.
Koi Herpes Virus (KHV) Every year sees multiple new outbreaks of this significant disease across the country, some in entirely new waters and some in those which have been affected before. Numerous cases have been recorded in Berkshire and the surrounding counties so no lake should be considered 'safe' as any remaining fish will potentially be carriers of the virus. Unfortunately the Environment Agency have reduced the 'disease controls' on affected sites from 5 years to 12 months so the full list of affected waters is effectively lost. This does not mean the disease is no longer a serious risk and it is still a 'notifiable' disease; in fact if anything it means it poses an even greater risk as put simply it means the control of the disease has not and is not being effective (partly due to no compensation so no enforcement) so they are not going to waste resources on it. Generally a summer disease as outbreaks usually occur at water temperatures between 15c and 25c.
Spring Viraemia of Carp (SVC) is another serious 'notifiable' viral disease of all carps and other species including tench, pike, roach, rudd, crucians and wels catfish. 2017 saw an outbreak in Arden, Warwickshire. A very significant disease especially due to the range of species it effects; outbreaks usually occur as water temperature rises above 7c with maximum mortalities between 10c and 15c.
Due to the continuing spread of the above diseases 'biosecurity' is of paramount importance. The "Check, Clean, Dry" regieme not only protects against viral disease but will also prevent the spread of other fish parasites and 'non-native' aquatic plant and animal species.
Any damp or wet fishing tackle or gear is a huge risk (not just landing nets) so make sure all your gear is clean and completely, thoroughly dry before entering onto the fishery. Thorough drying, ideally in sunlight, is the best form of disinfection. Net dips alone cannot be relied upon due to contamination, dilution, exposure time and the fact that many items are never dipped; it is not just about nets but also retainers, slings, mats, stink bags and even potentially moisture in tubing or in braid !. Anything, infact, that has been in contact with fish or the water.
Protect the Fish - Make absolutely sure it is all DRY.