The source of a buttery, fat-like substance that washed up on Whanganui's Castlecliff Beach remains a mystery, but laboratory tests will soon reveal its identity.
Samples taken were being tested by an independent laboratory, Horizons Regional Council consents monitoring team leader Pita Kinaston said.
Horizons received a complaint about the wash-up at 9.45am on August 8 via its Pollution Hotline, with a pollution response duty officer arriving at the Morgan St beach access about an hour later.
The samples were collected on the northern beach at the North Mole.
Kinaston said the officer found the substance at Castlecliff Beach at the Rangiora St and Seafront Rd end, while a small amount was also at the Longbeach Drive access.