An investigation into the incident is being led by Argyll and Bute Council’s Environmental Health team.

They say the plant — Hemlock Water Dropwort — was growing on the beach at Cardross and does not appear to have been washed ashore.

A spokeswoman from Parklea Veterinary Surgery in Helensburgh, said two dogs came into contact with a harmful plant – thought to be ‘poisonous parsnip’ – on last week.

FITS She said: “Both dogs started fitting immediately after consuming the plant. Within 20 minutes one dog died, while the second dog is still in a bad way.

“The plant must have been really toxic for a dog to have died within 20 minutes – that is really quick.

“We haven’t seen anything like this before here.” A spokeswoman from Lomond Veterinary Clinic added they have not had any similar cases, however they would advise walkers to keep their dog on a leash and monitor what they eat.

Word spread quickly of the incident via social networking in an attempt to alert animal lovers that there may be a danger to pets.

Alison Rutherford, member of Helensburgh East Esplanade Protection Group and a dog owner, said: “I have never heard of anything like this here.

“I am one of the beach cleaners and we usually find things like seaweed and sewage on the beach but I have never seen anything like this poisonous plant.” A spokeswoman for Argyll and Bute Council said: “This incident is being investigated by Environmental Health officers in Helensburgh in conjunction with Amenity Services and Police Scotland.

“The area affected is Cardross shoreline and the plant appears to be established rather than being washed ashore. Investigations are ongoing.

“Members of the public are asked to be vigilant whilst out walking their dogs and to be aware that poisonous plants do grow wild in the UK. Do not touch or allow children or pets to come into contact with any plant growing wild you are unsure about.”