Everything Surfers Need to Know About 
Polarized Surf Sunglasses
What do Polarized Surf Sunglasses Do?
Water surface with polarized Vs non-polarized lenses
Polarized surf sunglasses cut down on the amount of perceived light that is reflected off the water.  Glare can be a nuisance.  

When surfing near sunset on the west coast (sunrise on the east coast) you have to look in the direction of the sun to see the waves coming.  Although you would never look directly into the sun, surfers often find themselves looking straight into the reflection of the sun – which is nearly as bad.  
Polarized Sunglasses for Surfing
When you are sitting on your board looking at the swells coming in, the glare off the crests makes them easier to spot and to judge their distance.  With one eye, I find polarized lenses make it slightly more difficult to judge how steep the waves is which affects if, when and where it is going to break.  

Polarized lenses certainly don't make a day and night difference for judging waves but they do tremendously reduce glare so probably 99% of ocean goers prefer polarized lenses. 

Glare helps the brain calculate the steepness the wave face
Notice how different places on the wave reflect different amounts of glare.  The brain uses this information to calculate the steepness for different areas across the wave face.
Polarized sunglasses eliminate reflection off the water's surface
Since you cannot see sunlight reflected off the ocean's surface, it is much easier to see down into it.  This is why fisherman always use polarized sunglasses, it is easier to spot the fish.  But not seeing the surface of the water is a mixed blessing for surfers.
Polarized lenses can decrease the contrast across the surface of the ocean making the whole sea  look more similar.
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