You may have heard not to eat raw clams and mussels during the summer months. This is because during the summer months and sometimes during other seasons too, a phenomenon known as a red tide may occur. Red tides are caused by a sudden bloom of blue green plankton. Although the name suggests that the color of the water may be turned blue or green by the plankton the plankton is actually a reddish color, so it turned the water red. Some of these dinoflagellates produce a toxin. Normally this toxin is not in great enough quantities to harm humans, except during a red tide. Now here's where the shellfish come into the story, the shellfish can withstand the toxin by storing it in their digestive tract. When these animals are harvested for human consumption they may contain enough toxin to cause Paralytic Shellfish Poisoning. Paralytic Shellfish Poisoning may cause numbness, tingling, loss of balance, coordination problems, slurred speech, and in severe cases it may even cause paralysis or death.