More than half of litter fines handed out in Dublin in the last five years have not been paid.
Figures from the City Council also show the number of on-the-spot fines being issued is falling.
Mindy O'Brien from environmental charity VOICE said chasing litter-bugs for money ends up costing Councils.
Ms O'Brien said: "It costs a lot for county councils to bring the prosecutions forward.
"I have been told anecdotally that even when the county councils are successful, they don't recover the fees. Oftentimes, the judge would say 'okay, costs and fees are put into the poor box' or donated to charity, so they don't actually recoup some of their fees."