Dead shark, dirty nappies: op-shops say no

A dead shark, dirty nappies, a prosthetic limb, prawn heads and even someone's old dentures are among the bizarre donations being dumped on op-shop doorsteps.

These strange donations, which have also included empty paint tins, stained sheets and bald car tyres, were never put up for sale and just ended up costing charities millions of dollars on tip fees.

And Red Cross, Salvos and Vinnies stores have had enough.

To raise awareness and get people thinking about more worthwhile donations National Op-Shop Week, which runs from August 23 to 30, has been set up.

"Why anyone would think a dead shark is of value is beyond me," founder Jon Dee told AAP on Wednesday.

Mr Dee is urging people to look into their cupboards and find good quality items to donate during the campaign.

His advice: if you are considering giving something quirky, check with your local op-shop if it's sellable.

A good rule of thumb?

"If it's something you couldn't give to a friend, don't give it to an op-shop," he said.