Blue water in a pond may mean that the water is sterile. The colour of water is changed by what is dissolved in it. Living organic matter gives water a greenish tinge. Large amounts of inorganic particles, silt and iron, turn water a tea-like brown. Light bends as it goes from air into water.
Objects appear to be closer and shallower in the water than they are in fact.
Light tends to reflect off the water early and late in the day when the rays of sunlight are more slanted. Both these properties of water can be a problem for animals living on the surface. Hunting below the surface can be a problem when you are above the surface. Your prey is not where you see it. Also, it is more difficult to see a predator below the surface when so much light is being reflected.