The Collaborative International Dictionary of English v.0.48:

Murky \Murk"y\, a. [Compar. Murkier; superl. Murkiest.] [OE.
   mirke, merke, AS. myrce, mirce; akin to Icel. myrkr, Dan. &
   Sw. m["o]rk.]
   1. Dark; gloomy. "The murkiest den." --Shak.
      [1913 Webster]

            A murky deep lowering o'er our heads. --Addison.
      [1913 Webster]

   2. Obscured by haze or mist; clouded; turbid; as, poor
      visibility in the murky water.
      [PJC]