A survey by the Marine Conservation Society has found that levels of litter on beaches in Wales are rising steeply.
Over 30,000 items littered 25 beaches surveyed during the 20th annual Beachwatch Big Weekend in September 2013.
The MCS said the "shocking tide of litter" was a threat to visitors' safety.
Volunteers found more than 4,400 items of rubbish for every kilometre surveyed, a figure which the group said was far worse than the UK average of 2,309.
Figures were up 60% from the previous year and the MCS said levels were now at their worst ever.
Meanwhile, in Scotland there has been a drop in the amount of rubbish found strewn on the sands.
MCS Scotland programme manager Calum Duncan welcomed the downturn in litter levels but stressed that there is more to be done.
He said, "Despite a drop in litter amounts in 2013, this is still a shocking tide of litter which is threatening the safety of beach visitors both human and animal.
"After 20 years of campaigning it's disheartening that in 2013, in the UK overall, we are seeing worse litter levels than ever.”
Volunteers picked up an average of 1,963 pieces of litter per kilometre on Scottish beaches, where some of the items found included a set of rubber teeth, high heels and a bathtub.
The worst Welsh beach was Freshwater West in Pembrokeshire. Over 7,000 pieces of litter were collected there, while on Ogmore beach in the Vale of Glamorgan litter-pickers found half a TV discarded on the shoreline.
MCS Wales programme manager Gill Bell said, "It's coming in from the sea, being blown from the land or simply being dumped and dropped.”
However, Keep Wales Tidy said the findings were not a true representation of the country’s beaches.
Keep Wales Tidy chief executive Lesley Jones said, "We are very disappointed with the approach that MCS have taken with their beach survey and we think that the findings are inaccurate and misleading.
The charity claimed that weather conditions could have had a major impact on the survey.
They suggested that if the surveys took place on north-facing, totally tidal beaches, they would have shown no a litter problem.
Mr Jones added, "As an environmental charity in Wales, we are obviously not complacent and recognise litter ending up on our beaches that has been washed up from the sea, washed down our rivers or left on the beach is an issue that needs to be tackled, and we are tackling it.