Light-fingered patrons are taking advantage of the switch from plastic straws to metal ones in Wellington.

Just last month the city's waterfront went plastic straw-free, with 26 cafes, restaurants, and bars using alternatives or ditching straws all together.

But the move away from plastic has created a new issue.

Shake milk bar owner Aston Christie says last school holidays more than 20 metal straws went missing.

"We'll just say keep an eye on putting the milkshakes outside or making sure the straws are coming back or someone will clear a table and they'll be like 'No straws!'"

He says it's amusing people assume his metal straws are included in the cost of the shake.

"We find it so bizarre because where do you go in a dining experience where the cutlery is included with the meal?"

Poquito co-manager Ryan De Dominicis says he's having a similar problem.

"They just seem to be going missing. I'd say we're having to buy twenty per week. And they're not cheap."

Hospitality New Zealand general manager Rachael Shadbolt says even if people are doing it to make environmental changes in their own lives, it's still disappointing.

"If people have got those metal straws, we are actually reducing the use of the plastic ones, if they're using them in every day life. It's always disappointing because it is a cost."

"Sadly when you put something cool into the hands of the general public, sometimes things walk away and I would imagine that those metal straws are quite desirable."