Daytrippers showed "complete disregard" for one of Wales' most popular beaches by leaving "unprecedented quantities of rubbish", a council has said.
Barry Island attracted huge crowds to enjoy the record-breaking warm weather over the bank holiday weekend.
But they left the beach covered in plastic bottles, nappies and wipes - much of which was washed out to sea when the tide came in.
The Vale of Glamorgan Council said it drafted in extra staff to clean up.
But it said despite all their efforts to empty full bins as soon as possible, rubbish was just discarded on the sand.
Miles Punter, the council's environment director, said: "Huge numbers of visitors flocked to Barry Island to enjoy the warm weather over the bank holiday weekend and unfortunately some have shown a complete disregard for one of the Vale's most iconic locations.
"Unprecedented quantities of rubbish were left by day trippers and the council has had to bring in extra resources to deal with this problem.
"Enough is enough."
He said the council would be increasing its enforcement patrols over the summer period, with anyone found to be littering liable to be issued with a £75 fixed penalty notice.
They could also face being taken to court, and CCTV could be used to identify offenders, he added.
Rob Curtis, who runs the Friends of Barry Beaches group, said he was "shocked and appalled" when he saw the state of the beach on Monday evening.
"It was almost like a battle zone," he said.
"There were so many plastic bottles, nappies, things they had brought - all just left. I even saw buckets and spades and items of clothing.
"And you just think, most of that will get washed out into the ocean to pollute the marine environment.
"I just don't understand how people could come to a beautiful beach and leave it in such a state."
Some children were so angry about the rubbish they helped with the clean up.
Barry schoolgirls Nia and Amelie filled a number of bin bags in 40 minutes on Monday.
"And we only covered a small part of the beach. I've never seen so many wet wipes," said Nia's mother, Jodie May Davies.
Further along the south Wales coastline, people living in Porthcawl complained they too were faced with a messy aftermath to the bank holiday weekend.
Bins were left overflowing, with piles of rubbish left next to them, according to Martin Aaron, who lives in the town and is a keen surfer.
"The bins at Rest Bay were overflowing and seagulls were coming scattering all the litter," he said.
"I find it really depressing. There's a lot of people here now who want to see things change - we all try to pick it up but really the council should be emptying the bins more often."
Bridgend council said its staff had worked throughout the weekend to ensure the 220 bins in the seaside town were emptied regularly.
"We took away seven lorry loads of rubbish on Bank Holiday Monday alone, but it is still impossible for our crews to be everywhere at once," Councillor Richard Young, cabinet member for communities, said.
"So if you can see that a bin is already full, take your rubbish home and dispose of it there, or find another bin - don't just dump it and ruin the fun for everyone else."