How to Prepare for Open Water Swimming: A Pool Swimmer's Guide
You can hold your own in a pool. Open water is a different world. Here is how to cross from one to the other without getting a nasty surprise in the first fifty metres.
By the Swim Design Space Team · May 2026 · 14 min read
Open water swimming in the UK has grown sharply over the past few years. Events at Cotswold Water Park sell out months in advance. Local lake venues have expanded their supervised sessions. Forums, running clubs, and triathlon groups are full of people doing their first lake swim and wanting to know what to expect. The question that comes up most often is some version of this: I swim in a pool regularly, will I be okay?
The honest answer is: maybe, but not automatically. Competent pool swimmers get into difficulty in open water every season, not because they can't swim, but because they hit conditions they've never practiced for. Cold water tightens the chest before they expect it. The absence of lane lines and a pool floor creates an unexpected disorientation. The stroke that felt effortless at the leisure centre suddenly takes twice the energy in choppy, dark water.
None of this is a reason to avoid open water. It is one of the most rewarding forms of swimming available, especially in summer in the Cotswolds and Gloucestershire, where the venues are genuinely beautiful. But preparation matters, and most of it can be done before you ever get near a lake.
Why Pool Swimming Does Not Fully Prepare You
A pool is a controlled environment in every meaningful sense. The temperature sits between 27 and 30 degrees Celsius. The water is flat and clear. There are lane ropes to grab if you need a rest. The depth is consistent. The walls are always within arm's reach. The distance is measured precisely. You know exactly where you are and what you're doing at every point in the length.
Open water removes all of that, usually at once. The water is cold, dark, and moving. There are no walls, no lane markers, no clear floor. The buoys that mark the course look small from the water. Other swimmers in an event will be around you, sometimes very close. And the distance from the nearest solid object you can stand on can be several hundred metres.
This does not mean pool swimming is useless preparation — it is foundational. But there are specific skills that only open water practice develops: navigating by sight, tolerating cold, managing mild anxiety, and pacing correctly when you cannot push off a wall every twenty-five metres. Understanding the gap between pool readiness and open water readiness is the first step toward crossing it safely.
Cold Water: The Biggest Shock Most Beginners Don't Expect
Ask any experienced open water swimmer what catches beginners out, and cold water comes up every time. UK lakes don't warm up the way a heated pool does. In May, a Cotswolds lake might sit at 13 or 14 degrees Celsius. Even in July, the peak of the season, you're unlikely to find water much above 18 degrees. That's roughly the same temperature as your shower when you turn the hot tap to lukewarm.
When cold water hits the skin suddenly, the body reacts with what physiologists call cold water shock. The breath comes short and sharp, the heart rate climbs, and the muscles tighten. It passes within a minute or two for most people, but in that window a swimmer who has not experienced it before can panic, hyperventilate, or make poor decisions. The combination of involuntary gasping and trying to keep the head above water is where difficulty begins.
The most effective counter is simple: don't jump in. Wade in slowly from the shallows, splash water onto the face, neck, and wrists, and let the body adjust before submerging. This alone takes much of the sting out of the initial immersion. If you're wearing a wetsuit, it still helps — water gets between the suit and the skin and needs time to warm from body heat before it insulates properly.
Acclimatisation over time also matters. Cold water swimmers who go regularly through spring find the shock diminishes significantly by summer. Starting in May rather than waiting for a warm August day gives the body a gentler introduction and means you arrive at the best conditions already comfortable.
Cold water shock affects breathing first. You can partly inoculate against it by practising deliberate, controlled exhalation in the pool. After pushing off the wall, hold underwater for a two-count before beginning your stroke. Practise bilateral breathing so a tight chest on one side doesn't lock you out of your air supply. These habits don't replicate cold water, but they wire the breathing mechanics that steady you when the shock hits.
Sighting: How to Swim Straight Without a Black Line on the Floor
In the pool, navigation requires zero effort. The black stripe on the floor tells you where you are. The wall tells you when to turn. In open water, nothing does either of those jobs. Without active navigation, most swimmers drift. The human body is rarely perfectly symmetrical in its stroke, and over a few hundred metres even a small bias to one side produces a significant curve in your actual path. Studies with GPS-equipped swimmers have found that many recreational open water swimmers cover 10 to 20 percent more distance than the straight-line course simply from drift.
The technique that corrects this is called sighting. It involves briefly lifting the eyes just clear of the water surface during the pull phase of a stroke, finding a fixed landmark or buoy ahead, then turning the head to breathe and continuing the stroke as normal. Done well, it adds almost no drag and interrupts the rhythm only slightly. Done poorly, head fully out of the water, body lurching upward, it creates a body position problem that costs far more energy than the course correction saves.
The timing matters. The head lifts during the pull, not independently. As the leading arm sweeps forward and down, the chin comes up just enough to clear the water, the eyes find the target in a half-second, and the head rotates to breathe immediately after. The temptation is to hold the head up until you're certain of what you've seen. Resist it. Pick a large, obvious landmark, a tree on the far bank, a distant rooftop, a bright buoy — and trust your brief glimpse.
Most experienced open water swimmers sight every six to ten strokes. Beginners often do it less, assuming they're swimming straight. They usually aren't. Committing to a regular sighting pattern from your first session prevents the frustrating habit of swimming twice the required distance to cover a course.
Swim a length of front crawl with your head held up and eyes looking forward the entire time, like a crocodile on the surface. Your hips will drop and the effort will increase noticeably. This is deliberately exaggerated sighting — it builds the neck strength and body-position awareness that makes proper sighting more natural. Follow it with normal head-down front crawl and then practise lifting just the eyes to a fixed point on the far wall before turning to breathe. That is the movement you are training.
Build the Pool Skills That Open Water Demands
Bilateral breathing, efficient front crawl, controlled breathing under effort — these are the foundations every open water swimmer needs. Our adult lessons across Cheltenham, Gloucester, and Blakeney are run by Swim England qualified coaches who work specifically with adult learners.
Wetsuits: Do You Need One and What Should You Look For?
For first-time open water swimmers in the UK, a wetsuit is close to non-negotiable. Not because the rules say so — many venues allow skins swimming year-round — but because the difference between swimming in 14-degree water with a wetsuit and without it is substantial enough to determine whether your first experience is enjoyable or frightening.
A full-length open water wetsuit, typically 3mm to 5mm neoprene, does two things: it keeps the core temperature stable for far longer than skin alone would manage, and it adds buoyancy. That second point is underappreciated. A wetsuit in water provides a genuine lift to the hips and legs that makes body position easier to maintain. Swimmers who struggle to keep their hips up in the pool often find that their position in open water, with a wetsuit, is better than it ever felt in the pool.
A swimming wetsuit is not the same as a surfing wetsuit. The neoprene panels are placed differently, with more flexibility through the shoulders to allow a full front crawl arm pull without restriction. Using a surfing wetsuit for swimming is workable but uncomfortable over any meaningful distance. If you're investing in one, it's worth buying or renting one designed for the job.
Fit matters more than brand. A wetsuit that gaps at the neck lets cold water flush through constantly, negating most of the thermal benefit. The suit should feel snug but not constricting around the chest. Arms should rotate freely. Spend time in the fitting room pulling through the range of motion you'd use while swimming before committing to a purchase. Our swim training gear collection can help with the accessories that go alongside it.
Kit List for Your First Open Water Swim
You don't need much, but what you do need, you actually need. Here is what to bring to a first supervised lake swim:
Full-length, 3mm to 5mm, designed for swimming rather than surfing. Fit should be snug at the neck and flexible at the shoulders.
Tinted or mirrored lenses manage glare from the sun on the water surface. A wider field of view than standard pool goggles makes sighting easier. A secure fit is more important than any other feature — goggles that leak or shift under water are a significant distraction. Our adult swim goggles collection includes options suited to outdoor conditions.
An inflatable float on a waist leash, in orange or yellow, makes you visible to other water users and to the shore. It also functions as a rest point if you need a brief stop — float on your back against it and recover before continuing. This is now standard kit for solo and supervised open water swims.
Neoprene swim caps provide meaningful thermal insulation for the head. In water below 15 degrees, significant heat is lost through the scalp. Some venues provide brightly coloured silicone caps for visibility — wear a neoprene cap underneath if it's cold. Our swimming caps collection covers both.
Getting warm quickly after the swim is not a luxury. After cold water immersion, core temperature can continue dropping for several minutes after leaving the water. A full-length changing robe lets you get the wetsuit off and warm up without standing in the wind.
A flask of tea, coffee, or hot squash waiting by your bag costs almost nothing and makes a significant difference after a cold session. Drink it slowly after the swim while you change. It also gives you something to look forward to, which is genuinely useful psychological preparation for the first few cold entries of the season.
Safety: What the Pool Does Not Make You Think About
Pool swimming is one of the safest sports there is. The hazards are minimal, the supervision is generally good, and the consequences of getting into difficulty are manageable. Open water introduces a different category of risk that the pool simply doesn't train you to manage.
The two most important rules for beginners have no exceptions: never swim alone in open water, and only swim at lifeguarded or supervised venues until you have significant experience. These are not cautious overcorrections. A swimmer who gets into difficulty in a pool is almost always within reach of a wall, another swimmer, or a lifeguard. A swimmer who gets into difficulty in the middle of a lake is in a genuinely serious situation. The margin for error is completely different.
Cold water incapacitation is a separate concern from cold water shock. While shock is the immediate gasping response to entry, incapacitation sets in gradually as the muscles cool during the swim. Swimming ability is significantly impaired within ten to fifteen minutes in water below 15 degrees for most people, even if they feel fine. This happens faster than most beginners expect and is not reliably noticed until coordination and strength are already compromised. Keeping first sessions short — fifteen to twenty minutes maximum in cold conditions — is not timidity. It is how you stay in the water regularly rather than having one frightening incident that puts you off for good.
Blue-green algae is a seasonal hazard in some UK lakes, appearing as a scummy green or blue-green layer on the surface, usually in warm, still weather. It produces toxins that are dangerous to humans and dogs. Check venue notices before swimming and do not enter water with a visible algal bloom, regardless of how good it looked last week.
What to Expect From Your First Session
Most people's first open water swim is shorter than they planned. That is fine and entirely normal. The cold, the disorientation, the absence of walls, the effort of the wetsuit — they combine to make the first twenty minutes feel like more work than twice that time in the pool. Go in with a plan to swim for fifteen minutes and turn back early if it isn't feeling right. Leaving the water before you are exhausted is how you build a positive experience that brings you back.
Enter the water slowly. Stand ankle-deep for thirty seconds, then splash water on the wrists, back of the neck, and face. Wade to waist depth, bend forward, and wet the chest and face before putting your head under. This gradual entry takes three or four minutes and dramatically reduces the force of the cold water shock response. Swimmers who run in and dive under at a UK lake in May are making the experience harder than it needs to be.
Once you're swimming, the disorientation passes faster than you expect. The first width or loop of a course tends to feel uncertain — where are the buoys, which direction, how far — and by the second pass it already feels more familiar. Most swimmers report that by the end of a first supervised session, they want to go back. The cold becomes normal. The dark water becomes just water.
Do not judge your pace by your pool times. Open water front crawl is measurably slower than pool front crawl for almost everyone, partly due to conditions and partly because there are no push-offs. A swimmer who holds 1:30 per 100 metres in a pool might be closer to 2:00 or 2:10 in open water initially. This gap closes with open water practice, but it helps to know it exists rather than finishing a first session convinced that something has gone wrong with your stroke.
Where to Swim Open Water Near Gloucestershire
This part of the country is well-served for open water swimming. The Cotswold Water Park, roughly thirty minutes south of Cheltenham, is the largest freshwater lake complex in the UK, with over 150 lakes formed from former gravel workings. Several have dedicated open water swimming zones with marked courses, regular timed sessions, lifeguard cover, and proper facilities. It is one of the most beginner-friendly options in the country and is where many local swimmers take their first open water strokes.
Ashton Keynes and Somerford Keynes are popular entry points within the park. The lakes tend to warm faster in summer than deeper natural lakes, and the shallow margins make gentle acclimatisation entries easy. Some venues run coached open water sessions through summer, which are worth seeking out if you want structure and feedback rather than just turning up and seeing how it goes.
For those who prefer the sea, the Wye Valley and Forest of Dean area offer river swimming on warmer days, though the Severn itself is not suitable for recreational swimming due to currents and tidal range. The coast at Tenby and Pembrokeshire is accessible within two hours and offers some of the cleanest water in the UK.
Wherever you choose, check the Swim England open water hub for affiliated venues and planned events. Club open water swims run by affiliated clubs are an excellent way to make a first attempt in company with experienced swimmers who know the venue and can answer the questions you haven't thought of yet.
Why Your Pool Technique Still Matters Out There
Everything covered in this guide assumes you arrive at the lake with a reasonable pool foundation. Sighting only works efficiently within a front crawl stroke that already has a consistent rhythm and controlled breathing. Cold water shock is more manageable when your breathing is not already scrambled by a poor technique. The wetsuit helps your body position, but it cannot do much if your kick and body rotation are actively working against you.
Bilateral breathing deserves specific mention. Breathing only to one side in the pool is a common habit, and it usually doesn't cause significant problems over a length or two. Over three hundred metres in open water, it can leave you unable to see a hazard, another swimmer, or a turn buoy on your non-breathing side. Developing the ability to breathe comfortably on both sides, or every three strokes alternating, takes only a few pool sessions to work on and pays dividends in open water for the rest of your swimming life.
Efficient front crawl is also just less tiring over distance. Open water swimmers who thrash through a choppy lake with a wide, splashy stroke arrive at the far buoy depleted. Swimmers with long, smooth strokes and good body rotation arrive with energy to spare. The technique that makes pool swimming efficient translates directly to open water efficiency, which is why we keep saying that pool lessons for adults are not just for people who can't swim. They are for swimmers who want to get better at a sport they've already committed to.
Swim Better in the Pool. Swim Better Everywhere.
Swim Design Space runs adult swimming lessons across Cheltenham, Gloucester, and Blakeney. Small groups, Swim England qualified instructors, and sessions designed for adults of all levels — including swimmers preparing for their first open water event. Swim England Aquatics Champion 2024.
Frequently Asked Questions
Can I swim open water if I can only swim in a pool?
Pool swimming gives you the physical foundation, but open water requires specific preparation on top of it: cold water acclimatisation, sighting practice, and ideally a first session at a supervised venue with lifeguard cover. If your pool technique is still shaky, work on that first. The open water will be there when you're ready.
What is sighting in open water swimming and how do I do it?
Sighting is the technique of briefly lifting the eyes above the water surface to check your direction and find a landmark or buoy. It happens during the pull phase of a front crawl stroke — the head rises just enough to clear the water, finds the target in a quick glance, then rotates to breathe as normal. Most swimmers sight every six to ten strokes. You can practise the movement in the pool by looking up at a fixed point on the far wall before each breath.
Is a wetsuit necessary for open water swimming in the UK?
For beginners, yes, for all practical purposes. UK lake temperatures sit between 12 and 18 degrees through most of the swimming season. Cold water shock is real and affects even confident swimmers. A 3mm to 5mm open water wetsuit provides thermal protection and buoyancy, both of which make a first experience considerably safer and more enjoyable. Experienced skins swimmers exist, but building up gradually rather than starting without a wetsuit is the sensible approach.
What should I bring to my first open water swim?
Open water wetsuit, tinted goggles, a brightly coloured tow float, neoprene swim cap, a changing robe, and a flask of something warm. Tell someone where you're going and when you'll be back. Swim at a supervised venue with lifeguard cover for your first few sessions. Keep the session short — fifteen to twenty minutes is plenty to start.
How cold is open water swimming in the UK?
Significantly colder than most people expect until they have been in it. UK lake temperatures range from roughly 2 to 6 degrees Celsius in winter, 12 to 16 degrees in late spring, and 16 to 20 degrees at the peak of summer. Cold water shock can occur at any temperature below about 15 degrees. Entering gradually, wearing a wetsuit, and keeping early sessions short are the standard ways to manage it.
Where can I go open water swimming near Gloucestershire?
Cotswold Water Park near Cirencester is the closest and most accessible option, with multiple supervised lake swimming zones, marked courses, and regular sessions through spring and summer. It is around thirty minutes south of Cheltenham. For affiliated events and other venues, the Swim England open water hub lists everything in the region.
One Last Thought
Open water swimming catches people by surprise in both directions. Some pool swimmers arrive at their first lake session braced for something terrifying and find it manageable within five minutes. Others arrive confident after years in the pool and get a sharp lesson in how different the conditions are. The range of outcomes narrows considerably with preparation.
The things you can do now — work on bilateral breathing, practise sighting in the pool, buy the right kit, choose a supervised first venue, plan a short first session — are all genuinely useful. None of them require being fit or fearless. They just require doing them before you stand on the bank of a cold Cotswolds lake wondering what you've signed yourself up for.
If you want help with the pool side of things before you make the jump — front crawl technique, breathing mechanics, stroke efficiency — come and swim with us. The lake will feel a lot more manageable when the technique is already there.