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.
Woman charged over theft of campaigner’s car ‘must stay out of Belfast’
Bluetongue restrictions in Northern Ireland will be relaxed from Friday
Conviction led to safeguarding review at Presbyterian Church
Coroner vows to keep Noah Donohoe inquest ‘on track’ for January start date
Appeal to European Court being considered after ruling over Troubles disclosures