Answer
Our eyes are designed or used to see things clearly when our surrounding is air. When you are underwater, the index of refraction of the surrounding medium (i.e. water) changes. So, the focal length of the eyes also changes. Hence, everything is blurry. When you wear goggles, the surroundings of the eyes are air, so again we see things clearly.
Work Step by Step
Our eyes are designed or used to see things clearly when our surrounding is air. When you are underwater, the index of refraction of the surrounding medium (i.e. water) changes. So, the focal length of the eyes also changes. Hence, everything is blurry. When you wear goggles, the surroundings of the eyes are air, so again we see things clearly.
