Lake, Mere, Tarn and Water - The Difference

A question I am often asked in the hiking world especially when it comes to the Lake District. What is the difference between a lake, a mere and a tarn? You can go further and see that some lakes are called water, not lake. And when does a pond become a lake?

The famous trick question. How many lakes are there in the English Lake District? The answer (for pedants) is one. Well, one that is ‘called’ a lake, Bassenthwaite Lake. The rest are called mere and water etc like Windermere.

I thought it would be good to explain here a lot of the differences, whilst trying to not get too technical. There is a clue to a lot of it in the above riddle and answer, etymology. Our language and the naming of things has derived down the ages from so many influences from Vikings to Germanic for example. Let us take a look.

BaldHiker Retreats


A definition, a lake is a static or slow moving basin of water surrounded by land apart from the river or rivers that flow in and out of it. That’s it really. You could call nearly all of them all lakes technically.

The first question should be, what is the difference between a pond and a lake, when does it become a lake? There is no rule that defines it ‘properly’. The nearest scientific answer you get is a pond is standing water, and small enough to allow photosynthesis to rooted plants at the bottom. What we know as lakes, are too deep, too cold and the sun can’t get all the way down, so it is a lake not a pond.

So, the largest lake in England is? Windermere, here we go.


Windermere, Grasmere, Buttermere, Martin Mere to name just a few examples. Technically a mere is a lake that is really shallow in relation to its size (breadth). Take Martin Mere for example, if you have visited it you see a large body of water, yet its depth only ranges from 100 to 150 mm (4 – 6 inches.

Science will tell you also a mere is a lake without a Thermocline. Without trying to get too technical, a simple way to explain that is, think of a layer of water that separates the rough cold water at the bottom and the calm warm water at the top. It cannot occur until certain depths are in place and the temperature is right in the atmosphere.

Windermere is a complicated one because it is not as shallow as many meres and in ‘some’ warmer parts of the year it has a thermocline, but not always.

Etymology has played a part here too. The word mere comes from Old English ‘mere’ which meant lake or ‘sea’ in Old Saxon, a broad term for a body of water. Time and many many generations and language differences can make it all more confusing.

Take the Mediterranean Sea for example:

The Dutch say – Middellandse Zee

However the Germans say – Mittelmeer

Plus the Germans call a lake a sea, eg Bodensee or Zell am See in Austria

In language, mere and sea have diversified in time and geography, we just used it a certain way in general. A shallow but large lake.

reflections of boats on a mere


Hikers and walkers in Britain will know a tarn, high on the mountains and hills, a body of water that has been left over from the ice age. It is a lake, just a glacial lake. The word comes from Old Norse, Tjörn which meant ‘pool’.

tarn in the lake district

There are examples outside the Lake District for example Malham Tarn. Although I love that tarn, I will dispute the often used claim that it is the highest lake in Britain at 377 m. I would easily go for Red Tarn on Helvellyn at 718 m for starters.

For the pedants, weren’t Windermere, Derwentwater etc all glacial lake left over from the ice age? Are they tarns therefore? This is where etymology and geography and altitude have all played a part in the definition and confusion.


Derwentwater, Rydal Water etc. What about these beautiful and famous bodies of water. Lakes not called lakes but water. No science behind it, it all comes down to whoever named them way back in time most likely. Named as simple as possible.

ullswater an example of a lake called water

Bassenthwaite Lake

Let us go back one moment to Bassenthwaite Lake, the only ‘lake’ in the lake district and only because of how it was named. It was only called Lake since Victorian times!

Through history it was recorded as variations on Bastunthwaite Water and later Broadwater before only within the last couple of centuries changing to Lake on somebody’s whim. Perhaps a local land owner.

What About Lochs, Loughs and Llyns Etc?

Irish, Scottish, Gaelic and Welsh have all contributed to the many variations in names of our bodies of water in the UK.

Often, lakes in Wales are translated to Llyn (eg Llyn Tegid)

Ireland, Lough (eg Lough Neagh)

and in Scotland of course, Loch (eg Loch Lomond)

That is way too simple a definition of course. For instance in Scotland a loch is not just a lake but also a long sea inlet, that many would define as a fjord. A story for another day 🙂

loch lomond, a loch in scotland


For me, all the lakes are lakes and all have differing names thanks to our diverse history and cultures arriving over time. Forget what the name is on the map and go out there and enjoy the beauty of them all. A name cannot take that beauty and memories created, away from a place.

Share with your friends!
Subscribe to Our Newsletter

Similar Posts


  1. I grew up in the lake district and always thought it defined with whether it had a river feeding river exiting etc.
    For example, high mountain tarns seem mostly run off and rain fed. some onlt streams. Next you can explain rivers/streams/brooks etc

    1. Paul Steele says:

      Hi, you read my mind. Next info post for sure

  2. Hassan Hakeem says:

    I recently visited Lake District and thinking about to visit again in summer. I was searching on Windermere and came across with this readable article. i had a question in mind when I visited Grasmere, Windermere and Buttermere. Why aren’t they called lakes. Also I learnt something new Tarn totally new for me.

  3. Lorraine Hannon says:

    Thank you for sharing this. Stayed at a campsite very nearby, so read this
    with interest. Delighted to say, we walked here for a swim in the tarn, morning and late afternoon and had it to ourselves. The view in every direction is just ridiculously stunning.
    Bobbing in a tarn, no civilisation in sight, no sound but the wind and
    more view than your eyes can take in.
    Your suggestion was one of the best I’ve ever read.
    Thank you for something I’d have otherwise missed.

  4. Randy Ballard says:

    Very interesting article – Do you know if there might be a linguistic connection between mere and moor?

    1. Paul Steele says:

      Thanks. Now I have something else to look into haha

  5. Nice article! So it sounds like there is one lake in the Lake District (irony) and also one lake in the whole of Scotland. At least lake in terms of actually being named a lake. Bassenthwaite Lake and Lake of Menteith.

    I spent a lot of time on Bassenthwaite Lake as a child as my parents had a caravan there and later a log cabin.

  6. Thanks for sharing this information. I arrived in Lake District 3 weeks ago and as foreigner, I I was struggling to understand the differences among lake, mere and tarn!
    Thanks a lot!

    1. Paul Steele says:

      Hi Laura, it can be very confusing even for us so I thought best to get it explained a little. Thank you, glad we helped

  7. Peter J O'Rourke says:

    I shall call my shallow cove-side Annapolis estate “Baymere”

  8. I hadn’t heard of mere either. But, I am across the Atlantic “pond” lol and in the center of that. There is a park in Nashville, Tennessee, named “Grassmere.” It’s not that big, but is a small zoo. Mom and I discovered a love for otters there. I don’t recall any body of water, but then, that was about 30 years ago that we went. This article is VERY helpful!

    1. Paul Steele says:

      thanks for the kind words. Yes interesting the use has spread around the world in places 🙂

  9. Ursula (myVideoMedia) says:

    Thanks for the great overview. Mere was new to me.
    Perhaps you can add a Maar (Volcanic crater filled with water). You find a lot of them in the Eifel in the southwest of Germany.

    1. Paul Steele says:

      Thank you, yes great idea, I shall expand in future posts I think 🙂

Leave a Reply

Your email address will not be published. Required fields are marked *