A large and diverse group of organisms, algae are generally categorized as green, brown or red algae. They may occur in fresh or salt water, or any moist habitat, and vary from single-celled organisms to complex forms such as seaweed. Some serve an important role in medicines, cosmetics or industrial uses and others are valued for their nutritional value. However, blooms produced by some types of algae are dangerous to people and animals.
Red Tides
Algae called Gymnodinium breve produce blooms that cause a red discoloration of the water and have become known as red tides. The blooms produce toxins that may kill fish or be passed on to people who eat fish contaminated with the toxins. The toxins may produce gastrointestinal disorders, neurological damage or possibly death. Toxins from the algae may be released into the air and cause respiratory problems when inhaled.
Shellfish Poisoning
Shellfish may be contaminated with toxins from different algae that cause illness when eaten. Saxitoxins produced by algae called Alexandrium cause Paralytic Shellfish Poisoning. Symptoms include nausea, vomiting, diarrhea, abdominal pain, shortness of breath, confusion, loss of coordination or tingling of the lips, tongue, face, neck arms or legs. Another type of algae toxin produces Amnesic Shellfish Poisoning, which causes memory loss and confusion, according to the University of Maryland.
Ciguatera Poisoning
Small fish that live around coral reefs may become contaminated with the ciguatoxin produced from blooms of algae called Gambierdiscus. These fish are eaten by larger fish, which are consumed by people. The toxin may cause nausea, vomiting, headaches, numbness and memory loss. This toxin sometimes causes an unusual condition in which the sensation of temperature is reversed, so that cold feels hot and hot feels cold.
Blue-Green Algae
Even though it is classified as algae, blue-green algae are actually bacteria. Commonly found on ponds and lakes, its blooms produce toxins that are dangerous for people and animals that come in contact with the water or algae, inhale the toxins, or eat anything contaminated with the toxins. It may cause a rash, irritation to the skin or eyes, allergic reactions or gastrointestinal upset. In rare cases, it may cause liver damage, renal failure or neurotoxicity, reports Memorial Sloan-Kettering.
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