A mysterious grey sludge has been spotted stretching down a number of roads in Point Chevalier.
The suburb's Meola Rd, Jervois Rd, West End Rd, Pt Chevalier Road and Great North Rd have all been caked with the substance.
The culprit appears to be a rogue sucker that "dropped its load" along the many streets, Auckland Transport spokesman Mark Hannan said.
"The spill appears to be concrete slurry, probably from wash off, concrete saw cutting or concrete drilling," he said.