It has been estimated that of all documented great white shark attacks on humans, more than half have occurred within the Red Triangle. The area encompasses the beaches of the heavily-populated San Francisco Bay Area, and many people enjoy surfing, swimming and diving in these waters. Some have been attacked by great white sharks. The “Red” in “Red Triangle” refers to the red blood in the water, after a shark has made its attack.
Source: Wikipedia: http://en.wikipedia.org/wiki/Red_Triangle_(Pacific_Ocean)