Tarn Hows is the most photographed small stretch of water in the Lake District, and almost none of those photographs capture what's actually going on beneath the surface — geologically or ecologically. It's one of my favourite stops to slow down at, because the tidy, picture-postcard view is hiding a genuinely interesting layered history.
The hollow that Tarn Hows now sits in was carved out by glacial action during the last Ice Age. What was left behind, once the ice retreated, wasn't one tarn but several smaller natural pools sitting in that glacially carved ground.
In the 1860s, James Garth Marshall had those separate pools joined and enlarged into a single body of water, and planted the surrounding slopes with a mix of woodland specifically to create a designed, picturesque landscape. What you're looking at is a genuinely two-stage landform: glacial basin first, deliberate Victorian landscaping second.
Tarn Hows sits within a Site of Special Scientific Interest designation. The margins of the tarn support a range of wetland and aquatic plant species that need exactly this kind of undisturbed, gently managed shoreline to persist — which is the direct, practical reason swimming isn't permitted here.
The main loop is gentle and well-surfaced, but there are a couple of steeper sections with a noticeable gradient — the National Trust grades it as accessible "for some" rather than universally, and that's an honest description.
We pass Tarn Hows on both our Beatrix Potter tours. See tour details.