Seaweeds are algae that live in the sea or in brackish water. Scientists often call them "benthic marine algae", which just means "attached algae that live in the sea". They come in three basic colours: red, green, and brown.The present uses of seaweeds at present are as human foods, cosmetics, fertilisers, and for the extraction of industrial gums and chemicals.

They have the potential to be used as a source of long- and short-chain chemicals with medicinal and industrial uses. Marine algae may also be used as energy-collectors and potentially useful substances may be extracted by fermentation and pyrolysis.