Water is transparent to visible light. Still it is not possible to see objects at a distance in fog which consists of fine drops of water suspended in the air. This is so because

Fog consists of tiny water droplets suspended in the air [c1][c4]. While bulk water is transparent, these fine droplets act as scattering centers for visible light. When light rays encounter these droplets, they undergo Mie scattering, where the light is deflected in many random directions [t1][t6]. This process, known as multiple scattering, prevents light from traveling in a straight path from the object to the observer's eyes [t5]. Instead, the light is diffused and back-scattered, creating an apparent opacity or 'glare' that reduces visibility to near zero in dense conditions [t2][t6]. Unlike total internal reflection, which requires specific angles and interfaces, scattering is the primary mechanism for the poor visibility in fog [t5]. Consequently, the light is not absorbed but redistributed, making the fog appear as a translucent or opaque white/gray barrier [t2].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 10: The Human Eye and the Colourful World > 10.6.1 Tyndall Effect > p. 169
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 24: Hydrological Cycle (Water Cycle) > Fog > p. 332