Entry 04 · Water temperature

Below ten degrees: the thermometer, the clock, the afterdrop

Everything about how we swim between November and April is decided by a single number, and it is not the air temperature. The water reading is the only figure that changes the plan.

5.1°C at knee depth

Short swim, stated time

At the water: 9 November 2025
Typed up: 14 January 2026
Reading: 8 minutes
Where: Zarasai, Utena County

The number that changes the plan

The thermometer is a twelve-euro glass tube in a plastic case on a bootlace, and it lives in the front pocket of the bag. We read it at knee depth, about thirty centimetres down, held under for a full minute before anybody is allowed to trust it. Forecast apps that offer you a lake temperature are modelling a surface figure for a body of water that may well be the next lake along, and through October they have been out by four degrees in both directions.

The reading drives three decisions before anyone gets in: how long, how many at a time, and whether this is a swim or a dip. Ten degrees and above is a swim. Between five and ten it is a short swim with a stated time. Below five it is a dip, which means you get in, you go under, you breathe, you come out. Which of the three we are doing is written down every morning and said aloud, because the version carried in somebody's head is always the more generous one.

Said out loud on the bank

Read at knee depth, held under for a full minute
Ignore app figures for lakes; they model a different body of water
Above ten, swim. Five to ten, short swim. Below five, dip
Say the plan out loud on the bank before anybody undresses

A minute per degree is a ceiling, not a target

The guidance you hear everywhere, one minute in the water for each degree, is a reasonable starting point and a terrible target. It suits an acclimatised swimmer in still water on a windless day, and it takes no account of how much you have eaten, how long you stood undressed on the bank, whether you slept, or whether this is the first cold swim of the season after a mild fortnight. We use it to set a maximum, then take time off it for whatever the conditions are doing.

The factor people underestimate is wind. Five degrees of water under a still morning is manageable and, on a good day, pleasant. The same water with a nine-metre wind running the length of the lake strips heat off a face and a pair of hands at a rate that makes the identical duration genuinely unsafe, and the trouble it causes arrives after you get out rather than while you are in. Our winter times come off the water reading and get cut by a third whenever there are whitecaps.

Afterdrop, and the twenty minutes that follow

Core temperature keeps falling after you leave the water, usually bottoming out somewhere between ten and twenty minutes later, as cold blood from the limbs comes back to the middle. That is why the shivering starts on the bank rather than in the lake, and why somebody who felt perfectly well walking out of the water can be genuinely unwell by the time they are dressed. Everything we do in that first twenty minutes is arranged around the delay instead of around how anyone reports feeling.

The order is fixed and it is not up for discussion. Dry the top half first, hat on, top layers on, then the bottom half, then boots, then something hot and sweet drunk standing up and walking about. No hot shower, no car heater on full, no sitting down in a warm room half-dressed, because rapid surface warming pushes blood back out to the skin exactly when the core is at its lowest. The slowest dresser stands next to whoever is carrying the flask, and nobody leaves until everyone has drunk something.

The sauna afterwards, and how not to use it

There is a barrel sauna at the end of the jetty in the bay we use in winter, and it belongs to a family who let us light it on Sunday mornings. It has made our winters far more sociable, and it has also produced every one of our close calls, because a sauna hides the twenty minutes described above completely. It feels like proof of recovery. Somebody walks out of two-degree water into ninety-degree air, feels magnificent inside a minute, and has no way of knowing that their core is still going down.

We wait outside for five minutes, dressed, before anybody goes in. That feels ridiculous in January and it is the single most useful habit this group has. Nobody goes into the sauna while still shivering. Nobody goes from the sauna back into the lake, however good an idea it seems at the time. The reading, the times and who did what all go into the notebook before the door opens, because nothing accurate has ever been written down after the sauna.