This surveillance programme uses environmental DNA (eDNA) monitoring for species specific detection of Aphanomyces astaci spores directly from water filtrates. The presence/absence of eDNA from noble crayfish (Astacus astacus) and signal crayfish (Pacifastacus leniusculus) is also determined to supplement the results, and to evaluate the habitat status. Detection of noble crayfish eDNA, combined with the absence of eDNA from A. astaci and signal crayfish, substantiate the presence of non infected noble crayfish which constitutes the desired habitat status. These analyses are part of the collaboration and coordination with the national surveillance programme for noble crayfish. The geographic focus of the surveillance programme in 2022 is the Halden watercourse and neighbouring risk areas; the Mosse watercourse, Glomma watercourse, River Mysenelva and areas in the Eidskog municipality including the Buåa watercourse and the rivers Vrangselva and Finnsrudelva. Additionally, extensive monitoring (eDNA sampling and cage trials) were conducted in Buåa watercourse in 2021 and 2022 in order to evaluate the watercourse for disease freedom from A. astaci.

• In the Halden watercourse, eDNA of A. astaci was detected in the southern part of Lake Rødnessjøen and in River Hølandselva, within the control zone. eDNA of signal crayfish was also detected in the south of Lake Rødnessjøen, where there is a known signal crayfish population. All water samples in the risk area of the Halden watercourse region were negative for eDNA from A. astaci and signal crayfish, while most samples were positive for noble crayfish eDNA. No eDNA from signal crayfish was detected in River Lierelva in 2022.
• In the Mosse watercourse, no eDNA from A. astaci or signal crayfish was detected, while noble crayfish eDNA was detected upstream of Lake Langen.
• In the Glomma watercourse, eDNA from A. astaci and signal crayfish were detected at Fossum bridge, where signal crayfish were discovered in 2020. No eDNA from A. astaci, signal crayfish or noble crayfish was detected at the remaining stations in Glomma.
• In River Mysenelva, eDNA from noble crayfish were detected at two locations. No eDNA from signal crayfish or A. astaci was detected.
• In Eidskog, all samples were negative for signal crayfish and A. astaci, while several samples were positive for noble crayfish eDNA in the rivers Vrangselva and Finnsrudelva.
• In Buåa water course, no eDNA of A. astaci, signal crayfish or noble crayfish was detected in the extended survey in 2021-2022. Neither was A. astaci detected in the cage trials conducted in 2021-2022.

In summary, eDNA from A. astaci was detected within the control zone in Lake Rødnessjøen and River Hølandselva in the Halden watercourse, and at Fossum bridge in the Glomma watercourse. Frequent detections of noble crayfish eDNA within the regulated A. astaci control zones of the Halden watercourse, Mosse watercourse, and the rivers Vrangselva and Finnsrudelva in Eidskog, suggests the presence of vital noble crayfish populations within A. astaci control zones. The absence of eDNA from A. astaci and signal crayfish, and absence of A. astaci using cage trials demonstrates that Buåa watercourse meets the criteria for declaration of disease freedom. Thus, the Norwegian Veterinary Institute (NVI) recommends that the Buåa watercourse is declared disease free.