The most significant health problems caused by algae are paralytic shellfish poisoning, neurotoxic shellfish poisoning, ciguatera fish poisoning, amnesic shellfish poisoning and diarrhetic shellfish poisoning. Health problems cause by algae are typically caused by the consumption of contaminated seafood products.
Algae are considered toxic due to the naturally occurring toxins they produce. Toxic algae are found in coastal waters around the world, and all seafood consumers are at risk due to the international trafficking of seafood. Reporting of algae-related illness to the Centers for Disease Control is voluntary and therefore incomplete. However, evidence indicates half of all seafood intoxication comes from ciguatera, as of 2014.