A LYDNEY vet is warning dog walkers to watch their animals "very closely" to ensure they don't eat any unusual vegetation or fungi and fall victim to a mysterious poisoning.

The death of seven-year-old spaniel Sweep following a walk in Nine Wells woods, near Joyford, as reported in The Forester last week, follows a spate of up to 30 other dog deaths in woodlands elsewhere in England, all suffering similar symptoms.

The banned herbicide Paraquat, for which there is no antidote, was suspected of being the cause by Sundean Vets in Lydney due to the symptoms of shaking, salivating and diarrhoea. But no traces of the poison were found in a subsequent investigation by pest control officers or police in the area.

However, Mark Hinds from Severnside Vets in Lydney, said: "While Paraquat could cause the symptoms described, the similar cases investigated have failed to demonstrate a cause and it has been speculated that a natural poison such as a fungi may be involved.

He added: "Obviously the number of cases are very small, and while we happily still walk our own dogs in the Forest, I would recommend that owners watch their pets very closely and try to prevent them eating any unusual vegetation, as well as keeping their eyes open for possible dumped garden chemicals."

Deadly blue-green algae as well as poisonous fungi have been speculated as the cause of other deaths in areas such as Sherwood Forest in Nottinghamshire and other sites in Lincolnshire and the Queen's estate in Sandringham, Norfolk.

Tests conducted by Natural England following a previous spate of poisonings in 2009 failed to find any traces of manmade poisons, and some experts claim only a minute trace of blue-green algae is enough to kill a dog.