Officials with the Dublin San Ramon Services District said the stickers have long been the cause of clogged recycled-water irrigation sprinklers at local parks and other areas but they were only recently found to be the culprit, The Mercury News in San Jose, Calif., reported Monday.

"It started about a year ago and we didn't know it," said Sue Stephenson, a district spokeswoman.

Stephenson said a mechanic at the district installed a screen to catch the stickers, which had previously passed through the system due to their buoyancy, but the screen has to be vacuumed several times a day, creating a hassle and sparking environmental concerns, the newspaper said.

"They are the kind of our poster child to wage war against plastics in the wastewater stream," Stephenson said.

The mayors of the cities serviced by the facility -- San Ramon, Dublin and Pleasanton -- have entered into a wager to see which city can collect the most stickers over the course of the summer, the Mercury News said. The mayor of the winning city will supervise the two losers cleaning the screen in October.