What are the dangers of swimming in natural bodies of water? In essence I would like to know about all types of waters, but I am mostly interested in sea because it is most relevant to me. Like many people I enjoy taking a swim when at the sea side, and like many people I find that the stronger and bigger the waves the better. But then all the bad sea stories you've heard come back and it's really annoying, because what you constantly hear (at least when you're younger) is not how the sea works, but instead you hear threats and shallow warnings like 'if you swim too far off, the sea might pull you in'. The problem is I (and many other people I know) simply don't know anything about how the sea behaves.

Maybe you're aware of some bodies of work for lifeguards or something similar that might shine some light on the matter?

Note: The sea side I visit most often is Baltic Sea's south-eastern shore (Lithuania).

8 Answers 8


This is highly dependent on the type of water as well as the location, but I'll summarise a few things to be aware of. In many locations most of these dangers won't factor in, but they're useful things to bear in mind if you're trying to assess the danger of a particular body of water. I'll focus on the sea here - for other things such as rivers similar things apply (but there's obviously other things to look out for, different kinds of wildlife, waterfalls, etc.)

Currents: Yes, there are areas of sea that can "pull you in". (The same obviously applies for rivers here, but this is less commonly thought of with the sea.) More dangerously, there are also currents that can "pull you under". Similarly, and sometimes just as dangerously, there are areas of the sea that can "pull you along" the coast horizontally. This can sometimes be dangerous simply because it's much easier to miss, and can pull you into dangerous areas such as:

River outflows: Along the same guise as currents, but these can often hide at full tide and seem to appear very suddenly and strongly if you move into them.

Quicksand: Not often thought of when you're in the water, but if you decide to stay on the bottom for a while and hit a patch of this, it can root you to the spot.

Watercraft: Again, something that's often missed, but stray jetskis (for example) can seriously injure or kill you if they hit you full on.

Hidden depth: While you can often expect beaches to fall down at a gentle angle, there are often hidden areas that can suddenly drop away. While not an inherent problem if you're a good swimmer, these can often be associated with undercurrents too - so beware. Personally I'll only swim on beaches I'm familiar with at high tide (and have seen at low tide) to try and mitigate this somewhat.

Wildlife: This varies greatly - some areas can have deadly sharks (or similar) in them, and these risks go without saying! However, bear in mind more common things such as jellyfish (some of which will just give you a nasty sting and others that can be lethal) and crabs (which will give you a nasty nip if feeling threatened.) Know what lives in the waters you're swimming in, and be prepared accordingly.

Sharp rocks: This goes hand in hand with wildlife in that sharp limpets can also live on rocks, making matters worse - but just because the entrance into the water looks sandy, doesn't mean it is all the way through. If you swim at high tide and stay in while the sea recedes, you may find yourself painfully clamouring over all types of nasties. Same goes if an unexpected large wave throws you against such rocks.

Pollution: Like any body of water, you should be aware of pollution - especially after storms many runoffs will quickly head into the sea containing a variety of toxins and bacteria. In some countries / areas factories are still permitted to dump waste into the sea directly, in this case I wouldn't even risk getting in the water!

  • When to expect currents? How to deal with being caught in one? Commented May 22, 2013 at 12:37
  • 2
    @DominykasMostauskis Very hard to predict - the only sure fire way is to look up information beforehand. As for dealing with being caught in one, completely different question!
    – berry120
    Commented May 22, 2013 at 12:38
  • In addition, consider environmental pollution; for example, near urban areas, runoff after rainstorms may contain high levels of bacteria as well as chemical toxins. In fresh water in particular, there may be pathogens for schistosomiasis/bilharzia, cryptosporidiosis, typhoid fever, and other water-borne illnesses.
    – choster
    Commented May 24, 2013 at 22:08
  • England has some very shallow angled beaches. With high tide the sea rushes in, 1/2 mile at Cleethorpes. So you can find yourself a long way out. And with accompanying sea-fog, en.wikipedia.org/wiki/Haar_(fog) , people have got lost and drowned.
    – QuentinUK
    Commented May 2, 2020 at 14:42
  • 3
    Speedboats and Jet-skis have killed swimmers, even in areas reserved for swimmers, they like to go along the coast where many people sunbathe to show off and often kill swimmers or give them a fright.
    – QuentinUK
    Commented May 2, 2020 at 14:59

I have a couple of extra points that were always relevant for us as kids growing up in an extremely tidal area (peaking at 16knots - 30mph!):

  • Between islands, tidal races are usually predictable, and the local tide chart will let you know when slack tide (either high or low) is - these will be relatively safe times to swim. Halfway between these times the tide is at its maximum - which could sweep you rapidly away from your starting point.

  • Where there is a good surfing beach, you will find areas where the breakers do not come in - these are where the water brought in by the waves heads back out to see again. These can be very powerful and pull you down as well as straight out to sea rapidly.


I also would like to add: plants or sea 'wire' (hope that this is English). They tend to grow along the river banks and if your feet get strangled into it, it might be difficult to get your feet out of it, especially when the river flows.


Adding one more, from my own experience: a "false floor". I stepped into a lake fully dressed with shorts and sandals, because I saw it was just 10 cm deep. Unfortunately, what I observed as being the floor of the lake, was in fact the upper layer of plant growth... and the lake was, at this shore, in fact more than 1 metre deep (but shallow enough to stand). I got quite the surprise and learned my lesson.

I've been told this happens particularly at lakes with swampy shores.


While berry120's answer is spot on, I would like to add the following:

Overestimating yourself. A lot of times I see people swimming as fast as possible and as far as possible, either to show off of your swimming skills or just feeling invincible. Before entering any type of water consider your fitness level, e.g., maybe you're intoxicated.

Getting lost. A great example would be is swimming at night and forgetting where the shore is. Imagine that. I would be terrified.

Fellow humans. You really want to watch out for other people in the vicinity. You really don't want to disturb, get into way of, swim into someone. He or she might be angry, start a fight with you (yes, an extreme example, but this can happen, especially when we're talking about resort type of beach areas).

Weather conditions. Weather at the see can change rapidly, so one should check before hand, e.g., thunderstorms, high winds, storms.

Heat and Sunburn

Because the sun radiates off the water, a swimmer gets an increased amount of sunlight. The swimmer isn't always aware of this effect because the ocean depth keeps the water cool. Heat stroke, exhaustion, cramps, and burns can occur from excessive time in the sun.

Reference: link

Country borders. I remember one time reading of a fisherman(while fishing on ice) stumbling into another country's territory, so one should not swim close enough these type of borders.
Reference (in Lithuanian): link


Focusing on the dangers of Swift water [Rivers and even small streams]:

Many rivers and streams may look calm and inviting, especially in the hot summer, but can have hidden dangers.

Foot Entrapment Any time you are in water moving at over 2 kts [about 3.7km/h] if you get a foot trapped [in a rock, branch or what ever] and the water is deeper that your finger tips to your nose [think push-up position] you will drown unless you can get your foot free.

Hydraulics Faster flowing water has additional hazards. submerged rocks, and out cropping of shore may cause "Hydraulics", "Eddy Currents" and other invisible currents, if you do not have a good understanding of what to look for you may be unable to get to the shore, even in a small creek, or you may get sucked into a "hole" a churning current which can trap you in a vertical loop, letting you surface for just a second before dragging you along the bottom of the river, and repeating this until you get free or drown.

Sweepers When a tree has fallen into, or over a stream or river bank in such a manner its in somewhat perpendicular with the water, this is called a sweeper. If a swimmer gets entangled with a sweeper it can "sweep" you down and the water pins you to the tree or its branches, the most dangerous sweepers are fallen trees with many limbs, which can make it harder to self rescue.

There are many more hazards to moving water, I am by no means an expert, but even when the water is moving more slowly [in a pool, under a waterfall etc] many people die due to bad judgment. these pools look quite deep in relation to the rapids, but may be much shallower than they look. A swan dive into a rock, usually results in a broken neck, quickly followed by drowning. [near Vancouver Canada, I would estimate we lose upwards of 10 people every year, just on about 5 waterfalls]

Stay safe, and don't swim in rivers alone, or with out some understanding of the risks you may be taking. talking to locals helps, but its often the locals who drown, so treat there advice with caution.


Water temperature.

If you are used to swimming in public swimming pools, the water temperature is often controlled and always within a safe area (or the pool will have warnings or is closed.)

Natural water will come with whatever temperature nature provides, which is often colder than what man made pools are kept at.
Seeing others taking a dip is not a reliable guide, as people who swim regularly in the cold water can take a lot more than people who have never been in water that cold. And some of those people may wear swimming gear to handle the cold, which you may not have noticed.
Getting too cold is a very likely risk, and taking too many risks (other) risks because of that not uncommon.

An other problem with water temperature, more in ponds and lakes as far as I know, is the growth of dangerous algae, and the spread of dangerous bacteria when animals have died (in greater numbers) when the water gets hot. If the water you are hoping to swim is an often used one, you might find information, in local news sources or even on boards near the usual swimming beaches, but not every country does and not every swimming beach is likely to have one.


Not sure this was mentioned , in tropical waters, parasites. In the Amazon basin , piranha , electric catfish, etc. May be covered by "wildlife".

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