The wireless, high-data-rate transmission of information is becoming increasingly important for undersea applications that include defense, environmental monitoring, and petroleum engineering. Free-space optical (FSO) communication addresses this need by providing an undersea high-data-rate link over moderate distances (up to 100s of meters). Light transmission through seawater is maximal in the blue-green part of the optical spectrum (475 nm–575 nm), but turbidity conditions, which are dynamic, strongly influence the actual maximum. We describe the development of a laser-wavelength auto-selection algorithm and system for optimized underwater FSO communications. The use of a passive corner cube retroreflector allows all transmitter and receiver electronics to be collocated, which will be beneficial for any fielded system. First, we describe the laser test bed and retroreflector system. Next, we describe the development of the algorithm and hardware. We then describe the creation of various water types (from clear to turbid) in the laboratory using particle suspensions and dyes, which will enable wavelength-dependent transmission tests. Finally, we show experimental results from water tube tests, demonstrating wavelength auto-selection within one minute.