A large pile of share bikes dumped at a park in Sydney's eastern suburbs has underscored the challenges for operators and councils in overseeing thousands of the bicycles that have turned up on the city's parks over the past three months.

Passers-by found the bikes owned by Singapore company oBikes in a heap at Waverley Oval near Bondi Junction on Friday.

They were quickly picked up by oBikes staff but the circumstances around how they came to be stacked in a pile remains a mystery.

oBikes and Reddy Go, the first two "dockless" bike-share companies to launch in Sydney, say the problem of their bicycles ending up in the wrong places is not so much due to users but pranksters deciding to throw them in trees or waterways.