Algae checks start in North Island

Testing of some of the North Island's top trout and tourism rivers for the invasive "rock snot" algae will start today, biosecurity officials say.

Previously, Waikato regional council biosecurity officer John Simmons said the checks would start next week, beginning at Turangi, where the Tongariro River is a global Mecca for fly fishermen.

But Biosecurity New Zealand said the tests will begin today with priority given to significant waterways - including the high-value rivers on the volcanic plateau, and the Waikato.

Outside the Taupo, Tongariro and Turangi areas, a further 160 sites in the North Island will be surveyed next week.

About 73 per cent of rivers with the most suitable habitat for the algae are in the South Island.