Bull kelp is one of the largest brown algae. It grows attached to the sea floor by a specialized rootlike structure called a holdfast. From this, a long stemlike stipe extends to the surface of the sea, terminating in an enlarged, spherical, hollow float from which the linear leaflike blades emanate. It occurs on rocks in the upper sub-tidal zone to a depth of several fathoms throughout coastal British Columbia. (A fathom is equal to 1.83 m [6 ft].)