The NSW Environment Protection Authority has confirmed pesticides were present in the Hunter River at the time of a recent fish kill near Singleton.
The EPA has released an update into the incident, which occurred on 20 March, with water quality tests detecting pesticides in the river between Gowie and Liskintyre.
While chemicals were identified in the water, the authority says it is not yet clear whether they were responsible for the fish deaths, with formal fish autopsy reports still being assessed.
The EPA has confirmed there is no risk to human health and says all indications so far point to the incident being isolated, rather than an ongoing issue.
Investigations remain ongoing and are being treated as a high priority, with EPA teams continuing water sampling and following up information from the community.
