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British Phycological Society (BSP)
Working to advance education by the encouragement and pursuit of all aspects of the study of algae.
http://www.brphycsoc.org/
International Society for Diatom Research
Working to promote, for the benefit and education of the public, all branches of diatom studies throughout the world.
http://www.isdr.org/
Northwest Algal Symposium
Phycologists from the Northwestern United States and Western Canada: includes contact and activity information.
http://www.nwasalgae.org
Phycological Society of America
Scientific organization that promotes phycology, the study of algae, and fosters phycological research and education.
http://www.psaalgae.org/
Seaweed
This site has a lot of information on all aspects of seaweeds and marine algal biology.
http://www.seaweed.ie