The 6-foot-long, 115-pound "Waldo" underwater robot reportedly cost in the neighborhood of $100,000, and is used to help detect red tide.  It was first lost in late July, and was most recently heard from on August 31 -- with researchers receiving no reply from Waldo.  In addition to the actual cost of the robot, it also has a $30,000 toxic algae boom that is missing. 

The autonomous underwater vehicle has been in use since 2005, with the AUV expected to operate another few years.  It is able to search around-the-clock up to 30 days before it needs to be recollected for maintenance.

It's possible Waldo was struck by a boat or jet ski, suffered mechanical failure, or may be operating normally but is unable to send data back.  It's possible the circuitry inside Waldo is ruined if it sank too far and floated back to an operable depth.

A $500 reward has been offered for information about Waldo or its safe return.

There have been at least three boats with a dozen people searching the water for the past few days, and officials hope the search grows even bigger.  Mote Marine Laboratory officials hope they'll have a better chance of recovering the robot due to Labor Day weekend.