Three B.C. salmon farms have been quarantined since May 17 over concerns about a fish virus. (Chuck Stoody/Canadian Press)

A B.C. salmon farm forced to cull more than 560,000 fish recently because of a virus says the federal government has now quarantined another of its facilities.

The report by Mainstream Canada means the Canadian Food Inspection Agency has quarantined three salmon farms in B.C. in the last ten days over the virus known as IHN.

Mainstream Canada had to cull Atlantic salmon at its Dixon Bay site north of Tofino after the first quarantine was issued.

The company says tests revealed a "weak positive" result for the virus at another farm at Bawden Point, located in Herbert Inlet, also north of Tofino.

The company says it plans to harvest and process the salmon because they are mature and ready for market.

The virus does not affect humans who consume infected fish.

Earlier this week, Grieg Seafood announced a farm near Sechelt, which raises coho, was under quarantine because the virus was suspected but not confirmed. Further tests have come back negative

With files from the CBC's Curt Petrovich