Dog walkers at a Wirral beach became concerned when their pets fell ill after eating what is believed to be algae or seaweed washed up on the shore.
Facebook messages claim a pet has died after coming into contact with the mystery substance, although inquiries by the Globe have so far been unable to confirm this.
Worried residents alerted the local authority, whose environmental health officers visited the beach at Hoylake earlier this week.
The substance has been removed and sent to the Public Analyst to ascertain what it actually is.
The Public Analyst is a body of highly-skilled scientists who make up the frontline of the UK's public protection service where chemical analysis and tests are needed.
A Wirral Council spokeswoman said: “We attended the site on Monday after a member of the public reported a suspect substance on the beach.
"The substance was immediately cleaned up thoroughly by council staff and the following day a sample was sent to the Public Analyst for examination.
"We expect to have a report in ten to 14 days.”
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