Can carp see me on the bank?

What can a fish actually see out of water? When a fish looks up he sees the outside world though a round hole. Scientifically this is called ‘Snells Window’ which is a clear window of vision that allows the line of sight to travel out of the water and then bends to see parallel to the water as opposed to just above it. A bit like one of those funny mirrors you see on the rear window of a bus that can see the floor. It’s hard to explain it in a few words so if you have a look at the picture you’ll see exactly what I mean.

Inside the hole is visible and outside of that you can see a dark circle. The focus through the centre of the hole is clear as the fish is looking straight up, but around the edges it’s blurred. Outside of that hole it’s impossible for a fish to see out of the water as it only sees the reflection of the lake underneath. The higher up in the water a fish is, the bigger the hole and therefore clearer he sees, and if he is lower in the water his vision is more restricted and more blurred by the depth of water and also the angle of refraction. Add a bit of ripple to the surface and he struggles to see out with any clarity at all. The further out he is, the less likely he is to be able to see the bank so it’s a bit of a myth that carp can see every move you make. Fish have eyes on either side of their head so they do get quite a good range of vision but the majority of the time, factors such as colour and ripple make seeing anything with any clarity difficult unless they are very close in, high in the water, and the day is a clear one with little ripple.

As a basic rule of thumb, I draw a line at about 45-degrees from my head to the water line and anything inside of this is likely to be able to see me, whereas anything further out will struggle unless conditions are perfect. We do get a few flat calm bright days at this time of year where the fish are more likely to be up in the surface layers getting a bit of warmth, so if the water is calm and the sun is out, bear in mind the fish might be up in the water where spotting you will be much easier than normal. In winter they’re bedded down in the deeper water where they can’t see out as much and as it gets warmer the water is usually more coloured making it more difficult to see. Spring therefore is the time when fish are more likely to spot that you are harassing them so if ever there was a time for stealth, it’s now.