Spot checks by the council in Christchurch have revealed some yellow recycling bins are being filled with plenty of waste that doesn't belong there - including dirty nappies.
The council has been carrying out the checks in order to educate people about what can and cannot be recycled.
Thousands of recycling bins put out for kerbside collection across Christchurch and Banks Peninsula will be inspected, with those that pass the test getting a gold sticker placed on them.
Those that don't do so well will get a flyer with educational information dropped in the owner's letterbox. Bins that are heavily contaminated with non-recyclable waste won't be emptied that week.
The campaign comes as overseas markets toughen up on contamination.
Christchurch City Council's Ross Trotter says eight percent of contamination this week came from dirty nappies. Sixty-three percent was from soft plastic.
Trotter says lazy sorting can lead to a lot of rubbish heading to landfill instead of being recycled.
"If that truck tips a threshold of 10 percent that can't be accepted, then that potentially will go to landfill - all that recycling in that truck," Trotter told Newshub.
He said he suspected that some people simply don't understand the consequence of putting things in the wrong bin.
"Part of the issue may be capacity for families - if the red bin gets full and part of the overflow goes into the yellow bin."
The world's recycling processes were thrown into a spin in 2018, when China announced it would no longer accept the world's waste.
Previously, many countries paid to send their waste - mainly plastic - to China. However, the country effectively stopped the business in an effort to stop the deluge of contaminated materials causing environmental problems there.
The move caused a global shift as countries scrambled to find another way to get rid of plastics and other waste.