Unusually cool and damp weather conditions this spring in the coastal North Atlantic region provided the right conditions for a recent toxic algal bloom, also known as a 'red tide'. High concentrations of algae poison shellfish such as clams, oysters, and mussles. As these shellfish continuously filter the infested water, toxins build-up within their tissues, making them poisonous to humans.

The extent of the red tide this year has moved Massachusetts to declared a State of Emergency. Signs have been posted along the coast warning people not to catch and eat shellfish and the Northeast's shellfishing industry has come to a halt, with restaurants purchasing shellfish caught only in clear Canadian waters.

Though periodic outbreaks of the toxic algae occur in the coastal North Atlantic, this years bloom is the largest in recent history and has extended further south than usual.

Find out more:

• Red tides a danger to sea life (NPR)
• Massachusetts declares state of emergency over red tide (NPR)
• Toxic red tide hits New England shellfish (NPR)
• Red tide cripples New England shellfishing (NPR)