Waikato Regional Council scientists believe the deaths of large numbers of fish in the Waiomu Stream on the Coromandel Peninsula over the weekend are likely due to natural causes.

On Sunday morning the council received separate calls from two members of the public who reported seeing fish floating dead in the intertidal area of the stream, on the peninsula's west coast.

Two on-call incident response officers attended the scene to assess the situation and collect fish and water samples for testing to determine the cause of the deaths.

However, the council's senior water scientists say early indications are that the deaths are likely due to natural causes.

The council is also aware of a similar incident over the weekend at a different stream further north at Tapu.