Wave Graphic

What is "red tide"?

A "red tide" occurs when either natural or human factors cause a rapid increase in the production of one-celled organisms (dinoflagellates), which ordinarily grow in water rich in nitrogen and phosphorus. These destructive red tides, often resulting in what is known as paralytic shellfish poisoning, have occurred since biblical times but are becoming much more prevalent today. Sewage effluent and runoff from farms and lawns contain nitrogen and phosphorus. The dinoflagellates consume the nitrogen and phosphorus, when added to the oceans, and then reproduce or "bloom" profusely. They spread across the water like a carpet, absorbing oxygen and shutting off sunlight from plants. When these organisms die and decay, they absorb more oxygen, literally suffocating marine life.

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Last updated 31 December 1997

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