Keep Wales Tidy's annual report found the worst results for street cleanliness in the 17 years since the charity's surveys began.
Keep Britain Tidy said it was an issue right across the country and "only a small fraction of locations" in England were completely litter free.
Despite declaring "a litter emergency" in 2022, Keep Scotland Tidy also warned that litter levels continued to rise.
In Wales, the problem was found to be worst in towns and cities - with more than 35% of urban areas seeing "unacceptable" levels of litter.
There was also a 286% increase in the number of the most dirty streets, graded "D" for cleanliness.
Smoking-related litter and food and drinks packaging were the most common types of litter found.