A probe is continuing into the extent of the damage caused by a pollution incident on a tributary of the Moyola.
Dead fish were discovered on a two mile stretch of the Altagoan River, near Draperstown on Friday.
It’s understood the source of the problem has been traced to nearby premises.
A spokesperson for the Department of Agriculture, Environment and Rural Affairs says the investigation has been continuing over the weekend.
However bad weather has been hampering the probe.
Social media warning ahead of inquest into death of Noah Donohoe
Former senior police officer Jon Burrows confirms UUP leadership bid
Man’s body found in Cookstown in search for missing 21-year-old
Two taken to hospital following suspected gas explosion in east Belfast
Man critically ill in hospital following road crash in Co Tyrone n