No-one convicted of fly-tipping has been given the maximum punishment allowed, research by the Local Government Association (LGA) has found.
The LGA, which represents councils in England, said tougher sentences were needed to counter a 39.6% increase in fly-tipping incidents since 2012, to 997,553 in 2017-18.
Changes introduced in 2014 allow for sentences of a £50,000 fine or one year in prison for the offences, but these maximum penalties had never been imposed.
The LGA said the Government should review guidance to the courts to ensure the worst offenders face tougher sentences.
It said funding pressures meant council enforcement operations could not keep up with the growth in offences, despite having acted in 494,034 incidents in 2017-18, an increase of 70,000 in five years.
Martin Tett, chair of the LGA environment board, said: “Councils are doing everything they can to try to deter fly-tippers. However, prosecuting them often requires time-consuming and laborious investigations, with a high threshold of proof, at a time when councils face significant budget pressures.
“Consistent and hard-hitting prosecutions are needed to deter rogue operators and fly-tippers. Councils also need adequate funding to investigate incidents and ensure fly-tippers do not go unpunished.”