HONOLULU -- The mysterious brown stuff found in the ocean Tuesday off Kailua Beach has been revealed.

The dark patch was clearly visible from the shore.

State health officials determined it was sea sawdust which is a nickname for trichodemium, a naturally occurring bacterium in the ocean.

The bacterium feeds on nitrogen that leaches into the water from man-made products like fertilizer and then it blooms. As the nitrogen disappears, the bacteria die and decay.

The wind pushes the dead bacteria together making them visible to the naked eye and they can be brown, purple and even pink.

Health officials said this happened in 2008 off Makapuu, Waimanalo and Kailua.

They said sea sawdust is not a health hazard, but it can be an irritant.