Fish and Game in Southland says it's had reports that the disease responsible for killing kanakana or lamprey eels in the Mataura and Waikawa rivers may be present in four other rivers as well.
The jawless fish, which provide a valuable source of food for local Maori at this time of year, have been found with red coloured fins and contusions on their bodies.
Samples sent to MAF have been found to be infected with a bacterial disease never seen before in New Zealand.
An Invercargill-based senior Fish and Game officer Zane Moss says kanakana are part of Southland's culture and are important to Maori.
He says the disease outbreak serves as a timely reminder for all fishers to check, clean and dry all their gear when moving from one fishing spot to another.