Parents are being urged to put their children’s used nappies in the bin after a survey suggested one in 10 puts them in the recycling.
North London Waste Authority (NLWA) said lorry-loads of recycling have to be thrown away because they have so many nappies in them.
And recycling centre workers have to pull the filthy waste off conveyor belts by hand to ensure the effective sorting of other, recyclable, materials.
The authority estimates the problem costs it nearly £1.5 million a year.
It has launched a #BinYourNappy campaign to remind people to put used nappies in the general waste, after a Censuswide poll of 1,000 UK parents with children under the age of three found that 10% thought they went in a different bin.
Almost half of those quizzed thought biodegradable nappies were recyclable and more than two-fifths thought that was the case for compostable nappies.
The research also raises concerns about confusion over on-pack labels and logos, and the NLWA is urging manufacturers to make it clearer that nappies need to go into the bin.
NLWA chairman Clyde Loakes said: “It’s hard to over-estimate the scale of this unsavoury problem. We know parents want to do the right thing.
“That’s why we’re asking parents to put used nappies in the general waste bin.
“Contamination of recycling damages the environment, is costly for taxpayers and leaves recycling centre staff having to remove soiled nappies by hand.
“Our research shows that there is huge confusion about the labelling on packs.
“We’re calling on nappy manufacturers to come on board and make things clearer for their customers and help parents’ understanding.”
Steve Oulds, national commercial manager at Biffa Waste Services, which deals with recycling from households across north London, said: “We see millions of nappies arrive at our facility each year.
“Contamination is the single biggest challenge we face on a daily basis.
“Nearly half of parents in the survey didn’t know that recycling is sorted by hand. I hope that this knowledge helps encourage everyone to dispose of every nappy in the general rubbish bin.”