Kerikeri's water supply could be stretched this summer if an algal bloom persists in a lake which supplies most of the town's water.

About 70 per cent of raw water used for Kerikeri's town water supply usually comes from Lake Waingaro, a reservoir owned and operated by Kerikeri Irrigation Company.

The lake is west of Kerikeri airport, near the intersection of Wiroa and Lodore roads.

The Far North District Council stopped taking water from the lake last Monday after the irrigation company reported the presence of cyanobacteria, also known as blue-green algae.

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While tests for algal bloom toxins continue, water for Kerikeri's treatment plant is being drawn solely from Puketotara Stream, a tributary of Kerikeri River.

Council infrastructure manager Andy Finch said algal blooms often developed in rivers and lakes during warm weather and could produce cyanotoxins, which were harmful to human and animal health. Normal water treatment processes did not get rid of the toxins.

"We have tested water at the Kerikeri water treatment plant for cyanotoxins and have confirmed it is safe to drink,'' Finch said.

''We will continue to take water only from Puketotara Stream for another week and conduct further tests on the lake water to be absolutely sure no toxins are present. Only then will we resume taking from Lake Waingaro."

Regular tests for cyanotoxins would continue over summer to ensure the water was safe, he said.

A council spokesman said Puketotara Stream provided enough water to meet Kerikeri's current consumption.

However, on its own it couldn't meet peak summer demand, so restrictions would be implemented if it wasn't possible to resume taking water from Lake Waingaro.

Meanwhile, Kerikeri Irrigation Company would continue to supply about 500 customers from Lake Waingaro for irrigation purposes only.

It had notified its customers about the bloom and would keep them updated via its website. The species of algae detected was capable of producing toxin, but no toxin had been detected so far.

The Northland Regional Council is warning water users downstream of the reservoir to avoid using the water for drinking water — both stock and domestic — until cyanobacteria levels fall to acceptable levels.

Updates on cyanobacteria levels will be posted on the regional council web page as they become available.

A major algal bloom affected Lake Omapere, Northland's largest lake, in February. The bloom killed marine life such as eels and turned the water in its outlet an intense green.