Sea or reservoir. Which one might be safer?

I think we have a topsy turvy approach to hazard perception when it comes to outdoor swimming in the UK. It’s OK to swim at the coast where conditions continually change with the tide and weather, there are waves, obstacles and creatures that will sting you but it’s not OK to swim in inland water’s because it’s deemed too dangerous. In a flowing river (that very predictably will change when the forecast rain arrives), or the still, flat, non-moving water in a reservoir or lake, are the dangers so much greater than the sea that we need to restrict access?

I tried to demonstrate this oddness on a graph I created on scrap paper with the kids felt tips whilst I was frustratedly home schooling in 2020. Bored and fed up of the conflict of swimming locally. I have 40+ substantial bodies of water within an hours drive of my house in the Peak District, none of which I’m allowed to swim in because they’re all man-made reservoirs. Large, still, non-moving bodies of water. In large part, little different to a natural lake other than the man-made dam wall structure holding the water back. Often ringed by public rights of way, where the public are encouraged to enjoy nature, fresh air and our great British countryside. Permitted to look at the water but never, ever touch.

In the UK it’s common practice to rock up to the seaside and take a dip. No hassle, no questions asked. Dump your towel, strip off your clothes and head out into the salty sublime. No-one tells you to get out, get off my land, threaten to prosecute you for trespassing. At the coast we’re free to swim as we please.

Move inland and the hassle starts. That’s my water, you’re not allowed in. I have rights here, you don’t.  It’s not safe, you might die.

Rivers can be a mixed bag depending on where you are. Reservoirs and inland lakes (with the exception of the Lake District National Park) are the land of NO SWIMMING.

Sometimes the reprimands are hollered by landowners, often they’re from the mouths of by-standers, sailors, fishermen. Those who wish to exclude swimmers from the water. All too often because they don’t want to share the water but also to an extent because they genuinely believe it is very, very unsafe.

Such restriction varies across the country but by and large the picture is pretty bleak. It was the same when I started kayaking 25 years ago. Rather depressingly nothing has changed in that time. Access to inland waters has not become any easier. 25 blooming years!!!!!

As far as the “it’s not safe” message goes I believe there is some genuine concern that swimmers may come to harm as a result of swimming in a reservoir, river or lake. It’s not wholly surprising that such concerns abound. For 40 years we’ve been warned through water safety campaigns that inland waters are dangerous. The dark and lonely water advert from 1973 here was the start, I remember similar rhetoric from my childhood in the 80’s and similar campaigns have continued since. Campaigns that have focused on scaring people out of the water rather than educating them on how to be safe in and around inland waters. Extensive signage around many still water bodies warns of generic dangers. We have become a fearful and de-skilled nation as a result.

But are those inland hazards and risks as significant as they are made out. Are they risks that can be mitigated for and therefore avoided? Do we need to be excluded because the hazards are impossible to avoid? Is a still lake or reservoir more dangerous than the sea where we have the freedom to swim as we please?

Many inland outdoor swimmers will argue that the warning signs are poor. So generic that people start to question the validity of the information. That the signed hazards are over emphasised. Often incorrect (hey water company, that reservoir definitely get above freezing 😉). That those signs, whilst good to point out a potential hazard, aren’t a reason not to swim but a reason to be cautious, to be educated on how to mitigate for them and to enjoy a swim as a result. Many a swimmer walks past a “no swimming” sign nowadays. They have become so ubiquitous that their value as a means to protect the population from genuine harm is becoming null and void.

Head to Scotland and it’s a very different picture. Access to water is open via the Land Reform Act (Scotland) 2003 Freedom to Roam,as%20’freedom%20to%20roam‘. The warning signs still exist but there’s no “no swimming” sign plonked next to it. It’s ludicrous that I can drive 4 hours north and not worry about all of this.

And so, onto the actual point of this entry………….As part of my work as an open water swimming coach and guide, I hold a number of safety qualifications. One of the most useful ones I renew every two years is the Royal Lifesaving Society (RLSS) National Water Safety Management Programme. The course is designed for anyone who manages groups around and in water. Be they a school field course leader or like me an open water swimming coach. It focuses on the principles of keeping groups safe near water and breaks the hazards down by location. Inland (still water), rivers (moving water) and beach.

The data and information contained in the course materials are derived from the extensive experience of the RLSS team and draw on information from the Royal Society for the Prevention of Accidents (RoSPA) and the National Water Safety Management Forum.

I’ve read these documents a lot. The location specific sections vary in length. Still water covers 10 pages, rivers cover 14 pages, beaches take up 22 pages. Has someone been getting a bit of verbal diarrhoea or is that a reflection of the actual number and extent of consideration the hazards at these locations need?

Before I start on the actual hazards this quote is interesting from the documents:

The majority of drownings occur at inland sites. Due to open access and proximity to urban areas, rivers and streams account for two thirds of these drownings.

Significantly fewer people drown in the sea than at inland water sites. This is due to restricted access to the coast for much of the UK population and lifeguard supervision at many UK beaches.

So, the drowning stats between the coast and inland are influenced by how many people can actually access that water. The fact that the vast majority of the UK population don’t live near the beach and only occasionally visit it on holiday plays a part in the lower coastal drowning statistics.

There is indeed lifeguard supervision at SOME beaches. But not that many. I can think of vast swathes of UK beaches I’ve visited that have no safety supervision on them. And even where lifeguards are present they’re not there 24/7 and are only there in the summer season. Perhaps the extensive amount of safety education that is provided for coastal waters plays a part in the lower drowning stats? Maybe by allowing people to access the water at the coast, experience the risks first hand and learn how to manage them is a significant factor too.

The demographic of who comes to harm is also interesting. 78% of drowning victims are male. With a  big spike from the teens to late 50s. I think we’re all familiar with the headline “teenage boy loses life in reservoir”. There is a specific demographic who get into trouble in water. As a middle aged woman I’m certainly not it. In part because I choose to educate myself. In part because as a woman I think slightly differently to a man. We can’t get away from the difference in approach to life and mindset and that needs to be focused on rather than an overall “no swimming” line. Only by targeting and educating those specific at risk groups will we ever overcome those sad statistics.

Below I’ve pulled out the hazards identified for each location in the course documents. I’m not going to address how to prevent harm from any of these hazards, I’ve already tackled some of it on this blog before and there a lots and lots of resources out there already. The Outdoor Swimming Society’s content is particularly good, full of common sense and based on extensive experience within the OSS team

Common hazards

There are some general commonalities in hazard between all of the outdoor water locations in the UK. All of these can be hazards to consider at both coastal and inland locations.

Cold water. Outdoor waters in the UK can be cold with a range of 0-25C. That’s a big variation. For comparison indoor pools range from 27-33C. Where I am in the Peak District the surface of my local reservoirs hover around the mid to high teens in midsummer. That’s still cold water in comparison to average body temperature at ~37C. Any water below 37C will cause your body to cool.  The risks of cold water are cold water shock, cold water incapacitation and hypothermia. All can be overcome if you educate yourself and take necessary precautions to stay safe.

Deep water. As a swimmer I don’t want to scrape my legs on the bottom whilst I’m swimming. For a swimmer whether the water is 2m deep or 40m deep makes very little difference. I’ll still be out of my depth and unable to stand up and will need to have the ability to swim. The only significant impact deep water has is on water temperature. Deeper water can be colder. See point above on cold water as a hazard.

Water quality. Variable across the UK both at the coast and inland. Swimmers know this and take the risk, learn where is and isn’t clean enough to swim. Our water quality in the UK is disgraceful and is being challenged in other areas.

Visibility and underwater hazards. Many outdoor waters in the UK are murky and opaque. You can’t always see what’s underneath you.

Waterbed composition. Sand, silt, rocks, entrapment/entanglement. It could be the silty or rocky edge of a reservoir, or the rocks and sand of a beach. All a potential hazard if you’re unaware and don’t look out for them.

Banks and freeboards. The sides. The bits where you might need to get in or climb out. They could be high, steep, slippery or gently sloping and make a perfect access point.

Access/egress. How are you going to get in and out? See banks and freeboards above but also consider the movement of the water, a current in a river or breaking waves at the beach.

Water speed and force. Minimal in lakes and reservoirs, can be significant but variable in rivers, constantly changing at the coast. Water speed and force (the push it will have on your body) doesn’t follow the correlation you would expect. If water speed increases by two the force of that water increases by four. That’s a significant change, particularly at the coast where tidal speeds change during the tidal cycle.

Slips, trips and falls. In reality this could apply to any environment outdoors.

Other water users. Anglers, kayakers, powered craft just a few of the people hazards which may occur at any of these locations.

Hazard total = 10

Still waters

This includes all still water so, lakes, reservoirs, canals, ponds. Any non-moving body of water that’s outside.

Thermoclines. Layers of different temperature water that form in a still, non-moving water body. Water heats up from the surface. The top layer becomes warmer than deeper water or further from shore. That top layer can give a false sense of security leading people to think the whole water body is warm when in reality it may not be. This can lead to the risks associated with cold water mentioned above. They do not present a major hazard to well informed swimmers who know how to manage their swims in cold water. Swimmers are generally active in the top 2 m of the water and do not experience consistent deep cold water below. Thermoclines can be more of a risk to anyone who jumps in and may suddenly enter the deeper cold layer whilst submerged. This can induce an underwater cold water shock response which can be fatal.

Water movement in lakes and reservoirs. These are generally minor, created by inlets and outlets, surface waves and wind stress. Note that water movement and surface waves in this circumstance are small when compared to moving water and coastal surface waves.

Algal blooms. Common in some lakes and reservoirs at certain times of the year in the UK. The blooms can be toxic to animals who are more likely to ingest the water in significant quantities. For humans young children are more at risk as they are more likely to ingest water whilst playing. Algal blooms can cause skin and eye, ear, nose and throat irritation. Can be avoided and are not present year round.

Dams. It is notable that the course classifies dam structures specifically on their own rather than talking about them in the context of an entire reservoir. Dam structures can present hazards of strainers and turbulent and irregular water flow caused by water outlets. To me this suggests that the dam wall is indeed hazardous and to be avoided but the rest of the substantial body of water behind it presents no greater hazard than any of those identified above for still water.

Canals. Often suffering from lower water quality than many inland areas, variable water depths and turbulent and irregular flow around lock gates

Quarries pools and gravel pits. Can contain industrial scrap and industrial pollutants with irregular and unstable water beds and sudden drop offs. They can be dangerous, there are however some quarries and gravel pits which are well used for swimming and scuba diving.

Hazard total inland = 6



It is important to note that rivers vary hugely in their depth, width, length and hazards. There are many, many gently flowing rivers which do not contain many of these hazards.

Rivers and streams are often very cold. Colder than still standing water bodies. Moving water doesn’t stay still long enough to gain much heat from it’s surroundings. Higher up in water catchments rivers and streams can be very cold. Local reservoirs and lakes close to me are often significantly warmer than the river flowing close by. There is however significant variability, lower down catchments where rivers become slow leisurely, shallow affairs they can gain warmth from their surroundings and sometimes this relationship can be reversed. The important thing to remember is that rivers can be unpredictable in their temperature profile.

Water force and currents. As mentioned above water force, can vary widely. Shallow but fast flowing water can easily knock you off your feet. Deeper waters with currents, even if they look slow and non-turbulent from the surface can sweep you into more dangerous areas of a river or away from your exit point and safety.

Specific river feature hazards:

Eddies. Areas of usually calm water downstream of an obstacle. They can be a safer place to enter a river but they can also have a holding effect and be difficult to escape from.

Cushion/pillow waves. Created when moving water meets an obstacle. Can push you onto and pin you against the obstacle. Can also create undercuts leading to unstable banks or entrapment hazards.

Hydraulic/stoppers. Formed as water flows over an obstacle e.g. a rock, weir or waterfall. A re-circulating current is formed which pulls you back towards the obstacle. Can hold you in the hydraulic making you unable to swim to calmer safe water.

Strainers: Formed by partial blockages in the water. They could be formed by fallen trees and storm drain covers. A swimmer can be held against them by the flow of water

Undercut rocks and banks. Unstable banks leading to accidental falls or collision from falling material. Can create an entrapment hazard as tree roots are exposed and act in the same way as a strainer

Weirs. Man-made structures designed to control the flow of water. They can create very stable and powerful hydraulics, see above.

Flooding. Water levels vary in rivers all of the time but at time of flood events the hazards increase. Increased levels of pollution and debris are seen, water force and currents can be significantly greater sometimes with surges, the water bed can change rapidly and unpredictably. Easily avoided by just not entering water when in flood.

Hazard total river = 9


Specifically quoted from the course materials “The coastal environment, in particular where the sea meets the land, is one of the most dynamic on the planet………..Ultimately the beach can be a hazardous play ground, especially for young or uninformed people who see the attraction but often do not appreciate the dangers associated with beaches.”. Note there is no such corresponding statement in relation to inland still or rivers. Beaches are specifically highlighted for their potentially hazardous nature. Beaches are constantly changing, dynamic environments.

Waves: breaking (spilling), dumping and surging. Dumping & surging waves can knock you off your feet. This can incur impact injuries and can result in spinal/neck injury

Backwash can pull you back towards the incoming waves, making it difficult to get out of the turbulent surf zone.

Rip currents. A channel of water moving out to sea, often in the surf zone.

Rip currents are believed to be the largest cause of coastal drowning, taking swimmers out to sea. Rip currents can travel at 1m/s meaning a simmer can be carried out 60m in one minute. Rip currents can pulse, fluctuating between high & low flow rates. Therefore easily catch people out.

Flash rip currents appear & subside rapidly and can occur in fairly flat conditions taking people by surprise

Tides. Constant rise and fall of the water at the beach. Tides can cut swimmers off from exits from the beach. Both incoming and outgoing tides can create tidal currents that can transport swimmers out of safety zones.

Longshore currents. Swimmers can be carried along the shore by longshore currents and find themselves in rip currents.

Sandbars and holes. Often created by longshore currents as well as wave action. People can be cut off on sandbanks and holes create irregular sea beds resulting in water users finding themselves suddenly and unexpectedly out of their depth. They are also often the cause of rip currents, see above.

Effects of wind and weather. Weather can change rapidly in the UK. Due to the large expanse of water and open-ness of a coastal environment, changes in wind and weather can have a sudden and significant effect on conditions.

Offshore winds cause water users to be swept away from shore and out of depth, sea conditions during offshore winds can often be relatively calm leading users to be unaware of the risks. Onshore winds can create bigger more powerful waves. High winds can create poor visibility due to water spray from turbulent water.

Water temperature. The coastal water temperatures in the UK rarely rise above 18C. Worth noting that this is lower than the overall figure quoted up to 25C earlier in the course documents. From experience the coastlines around the UK I visit are always cooler in summer than the inland waters I use. Over winter the picture reverses with the sea remaining slightly warmer than inland waters (still well below 10C though!) This is a result of larger water bodies taking longer to cool down/warm up.  The sea is a larger volume of water than a lake.

Man made structures. Piers, sea walls, flood defences, groynes. Man made structures can create rip currents, irregular water flow, increase irregularity of the seabed due to non-natural erosion and can create a collision risk.

Pollution and debris. Whilst pollution and debris is a potential hazard at all outdoor water locations it is specifically picked up in relation to beaches due the quantity of pollution and debris that can be washed up on shore. Many beach sites have well known and established raw sewage outflows on them. Specific risks highlighted include; weils disease, eye, ear and skin infections, chemical poisoning, respiratory infections, septiceamia, physical injury and entrapment, diarrhoea, fever and vomiting.  

Marine life. Various animals in the sea can cause a swimmer harm. Weaver fish, rays, sea urchins and jellyfish are specifically referenced in the course documents.

Hazard total coast = 10

In summary, what I gain from these course documents is that the coastal environment contains the greatest number of specific hazards (10) and is the most dynamic environment, constantly changing as a result of tides and weather. Whilst hazards are of course identified for inland moving (9) and still waters (6) to me they seem far more predictable and, in the case of still waters, significantly fewer than at the coast.

So what do you make of this?

I’ve swum at the coast and I know many, many people who swim in the sea regularly and safely. With correct hazard understanding and risk management it can be a safe place to swim. I’ve swum in many rivers, lakes and reservoirs too. They all have their own risks, things to keep you on your toes. I have to say though give me a still, non moving piece of water any-day for the calmest, most switched off swim I can have………….unless of course there’s a shouty human on the bank 😉

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