Is nostoc harmful to dogs?

While nostoc itself is not inherently toxic to dogs, some species of nostoc can produce harmful toxins (such as microcystins), which can pose a danger to animals if ingested. Dogs that ingest large amounts of nostoc may experience gastrointestinal distress, and in rare cases, exposure to toxins could lead to more serious health issues. It is best to prevent pets from ingesting nostoc or coming into direct contact with large amounts of it, especially if you suspect it might be producing toxins.