A dog has died after eating a white waxy substance washed up onto the beach at Polzeath.
The incident took place last week, and has prompted Cornwall Council to issue a warning to keep pets and young children away from any similar material found on the coastline.
Warning signs have been erected at Polzeath.
David Owens, the authority's Assistant Head of Environment and Waste Management, said: "Following reports of white and yellow waxy substances being washed up on a number of South Cornwall beaches in October, the Council has been informed of a similar white waxy substance being washed up on Polzeath beach.
"The authority was informed of the incident following the death of a dog on 11 December and immediately erected warning signs on the beach.
"This is the 14th report of substances being washed up on beaches in Cornwall over the past two months and staff from the Council are working closely with the Maritime and Coastguard Agency, Environment Agency and Natural England to monitor the situation and are on stand by to take further action if required.
"Members of the public are asked to report any sightings of substances being washed up on any beach in Cornwall to the Council as quickly as possible and to ensure that children and dogs are kept away from the material." z