One dog had to be rushed to the vet after eating some near the carpark at the Pembroke end of the beach.
A second pile was found on the pathway to another nearby carpark.
“[Raisins] are toxic to dogs if eaten so please take extra care if in that area,” said a spokesperson from Vets4Pets, which treated the dog. “As few as four-to-five grapes can cause death in an eight kilogram dog so please be extra vigilant.”
Symptoms of poisoning including vomiting, diarrhoea, lethargy and tremors. Vomiting should be induced immediately if an owner suspects their pet has swallowed grape or raisins.
It is unclear why the raisins have been left in the popular dog-walking spot.
Express has attempted to contact the States Vet for further advice.