Vets in the area say the dogs have suffered vomiting and diarrhoea after walking along the coast in recent weeks.
Yorkshire Coast Pet Care said it has been "inundated" with cases and advised owners to avoid the beaches until environmental health experts can figure out what is causing this illness.
Cath Baggins said her working cocker spaniel Roo became ill the day after visiting Fraisthorpe Beach, near Bridlington, on December 30.
Roo spent six nights at the vets, after prolonged vomiting and diarrhoea led to dehydration, but she is now recovering at home.
“We just went into panic mode, thinking she’d eaten something and it had poisoned her,” Ms Baggins said.
“I thought we might lose her because the vets couldn't tell us what was wrong and this diarrhoea just didn't stop.
“It (the beach) is my favourite place to go and it's my dog's favourite place to go, but I don't know if I'll dare go again.”
Veterinary nurse Brogan Proud said she works at practices across North Yorkshire and she has seen “tonnes” of dogs suffering with this mysterious illness.
She said: “I'm personally not taking my dog on the beach for the next couple of weeks and if your dog shows any symptoms of vomiting or diarrhoea I would get onto the vet straightaway.
“The sooner that they've had this injection that helps them stop vomiting, the sooner they can start getting better.”
She added: “None of the ones that I've dealt with or heard of firsthand have died.
“With an anti-sickness injection, something to settle the stomach and help with the diarrhoea, and a rest at home, they tend to pick up within the week.”
She is urging owners to alert their local council if their dog falls ill after walking on the beach.