How Is Open Water Swimming Different From The Pool?


Every year we ask our swimmers (just before they enter the water) to put their hands up if it’s their first open water swimming event and a sea of hands shoot into the air. For some it’s even their first ever (proper) dip into the open water, so if it’s your first event then rest assured you’ll be in good company.

To give you a base understanding of how open water swimming differs to your local pool, we’ve pulled the below guide together for you. 


Most indoor pools are maintained between 26 and 31 degrees Celsius, whereas open water can be 0 degrees, or even slightly below in the sea. In the summer, rivers, lakes and the sea around the UK will range from low double digits up to the low 20s. This means that at its warmest, open water in the UK is cooler than a swimming pool. It can still feel chilly when you first jump in to a pool, so the ‘cold’ aspect of open water swimming is not as big a barrier as you might think… plus cool water on your skin feels amazing so learn to embrace it! 


If your swimming pool water is cloudy, it probably means something has gone wrong. Outside, your visibility in the water can be close to zero.  Low visibility does not mean poor quality or unsuitability for swimming – even when the clarity is good, you often still can’t see the bottom, so it seems as if visibility is poor. Just remember, you don’t need to be able to see underwater to be able to swim! 


Open water is natural; that means it has things in it such as fish, plants, insects, bacteria, etc. Many of those things will do you no harm; healthy water should have plants and fish and their presence is a good sign. Swimming pools are dosed with chemicals and full of sweat and urine. Your local swimming lake might seem more enticing once you think about that!  


In the pool, water depth is regular with signage to distinguish shallow and deep ends, but no such regularity exists outdoors. Swimmers should be cautious of shallow water as much as deep water – take care when entering the water ensuring there are no obstacles. Once you are out of your depth, it really doesn’t matter how deep the water is as it doesn’t affect your swimming, however, swimming in deep water can take a bit of getting used to. Remember that you are not surrounded by walls that you can reach within a few strokes; this is one of the things that gives you that great sense of freedom when you swim outside! Consider slowly building up your confidence. 


Water in pools barely moves, whilst open water can move faster than you can swim. In order to stay safe, you need to know what’s happening in any body of water you swim in. It is often obvious if river water is flowing fast but it can still be difficult to gauge exactly how fast and what the implications are for swimming. If you are new to outdoor swimming, stick to rivers where the flow is less than your swimming speed, and always swim upstream first if you plan to get out at the same place you got in. Note the flow in some rivers can change very rapidly after heavy rain or if they are controlled by dams. 

Water flows in lakes are generally benign, but look out for in-flowing rivers and outflows. The sea is totally different and must be treated with the utmost respect. Speaking to an experienced swimmer with local knowledge is highly recommended before swimming anywhere except a lifeguarded beach. 


Except for rare calm days, the water surface of rivers, lakes and oceans is rarely flat. Swimming in choppy water can be challenging and fun, but it’s also more difficult than swimming in the calm conditions of an indoor pool. You will get tired more quickly when swimming in rough water, and you will find it more difficult to see where you are going, so always stay well within your capabilities. 


Swimming outdoors with the sun on your back ranks as one of life’s most pleasant experiences, but do remember the sun can still burn you while you’re in the water. Outdoor swimmers often end up with intriguing tan lines! Use a good, waterproof sunscreen. 

Hopefully reading this blog will give you a good dose of knowledge and a boost of confidence when you first take the plunge. And remember, our crew, lifeguards, and kayakers will be with you every stroke of the way.  

We do recommend that all Great Swim entrants have at least one open water swim practice session before the big event. Search for a local open water swim club or use the Outdoor Swimmer website


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