More than 47,500 dogs were abandoned by their owners in the UK last year, figures from the Dogs Trust suggest.
The animals all ended up in council pounds and more than 5,000 were later put down, according to the charity's annual survey of 345 local authorities.
In total, 102,363 strays were picked up by UK councils in 2014-15 - a fall from 110,675 dogs in 2013-14.
Councils were having to put healthy ones down due to "a lack of space and resources", the Dogs Trust said.
Of the 102,363 stray dogs picked up last year, 54,767 were reunited with their owners, the charity said, but 47,596 dogs were never picked up.
Dogs Trust said it also had handled 43,771 calls from people trying to give up their dogs in the last 12 months.
The charity said it was hopeful the number of stray pets returned to their owners will rise once it becomes a legal requirement from April for dogs in England, Scotland and Wales to be microchipped.
But Adrian Burder, chief executive of the Dogs Trust, said it was time for people to stop treating family pets as a "disposable item".
"Abandoning a dog is simply unacceptable and sadly, Dogs Trust's famous slogan 'a dog is for life' is as significant as ever," he said.
"If you are not ready to care for a dog for its entire life, do not commit to becoming a dog owner.
"This year's... survey shows that local authorities continue to pick up the pieces and have found themselves in the tough position of being forced to put healthy dogs to sleep for lack of space and resources."
The charity said 319 local authorities in England Wales and Scotland responded to its survey, as well as 26 councils in Northern Ireland.