Why You Shouldn't Swim on St Elijah's Day, and Is There a Real Explanation Behind the Old Belief?

"Until Elijah's Day, the peasant swims; from Elijah's Day, he bids the river farewell." Even Russians who have never set foot in a church know this saying. But where did it come from, and why does it still ring true?

Every year on August 2, the feast of the Prophet Elijah, known in Russia as Ilyin Den (Ilya's Day), the same argument flares up online. Some are convinced that after Elijah's Day you mustn't go in the water: maybe because of devils in the river, maybe because the water is icy, or maybe just because "that's the way it is." Others wave it away as mere superstition.

Interestingly, both sides are right, but each only half right. Behind the folk belief lies not mysticism but the keen observation of people who lived beside water for centuries and noticed what we now call phenology.

What Tradition Says

In folk belief, the Prophet Elijah is the lord of thunderstorms. Thunder is the rumble of his heavenly chariot, and lightning the fiery arrows he uses to strike down evil spirits.

According to the belief, devils and water spirits, fleeing from Elijah, hide in the water: in rivers, lakes and ponds. Anyone who goes for a swim risks running into them. The consequences, according to our ancestors, ranged from illness to drowning.

The second part of the belief is seasonal. Elijah's Day was considered a boundary: "summer until lunchtime, autumn after lunch." From this point on, the nights grow noticeably longer, the water cools and the swimming season ends. Peasants switched to the harvest, and there was no time for the river anyway.

Perun in a Cassock: Where the "Thunderous" Saint Came From

The Prophet Elijah is an Old Testament figure who, according to tradition, lived around 900 BC. He denounced King Ahab for worshipping Baal, called down fire from heaven on Mount Carmel and, according to the Bible, was taken up to heaven alive in a chariot of fire.

That chariot made him the ideal "stand-in" for Perun, the Slavic god of thunder and lightning. After the Christianisation of Rus, missionaries didn't so much stamp out pagan festivals as dress them in new clothes. Perun's Day fell on the same dates (July 20 in the Old Style calendar, August 2 in the New Style), and the attributes matched: a chariot, fire and power over thunderstorms.

Religious studies scholar Alexander Neveev notes that the image of Elijah, who "rides across the sky during a thunderstorm and kills devils with lightning," may be a trace of ancient myths, although just how ancient remains a matter of debate.

So pagan rites — bratchiny (communal feasts) with ritual beer, a sacrificial bull and ceremonial bonfires — flowed smoothly into the church feast. And the ban on swimming, which may originally have been part of a pre-Christian ritual cycle, got a new explanation: now it wasn't Perun's spirits hiding in the water, but devils fleeing from Elijah.

What Actually Happens to the Water in Early August

The folk belief turns out to be more accurate than it seems: it just works through physics rather than evil spirits.

The Nights Grow Longer

By August 2, the day in Moscow is already an hour and a half shorter than at the summer solstice. The sun sets earlier and rises later, and bodies of water take in less heat during the day than they lose overnight. It's in early August that the balance starts to shift: the water is still warm from momentum, but the trend is already downward.

The Temperature Drops Fast

In early August, the water in lakes and ponds around Moscow stays at around 24–25°C. By mid-month, it's down to 19°C. And by the end of August, some bodies of water cool to 13°C.

A drop of 6–12 degrees in three to four weeks isn't gradual cooling but a fairly sharp turning point. And it begins precisely in the first days of August.

The Thermocline

In still waters, lakes and ponds, a distinct temperature layering forms by August: the surface water is warm, but at a depth of one and a half to two metres it can be 8–10 degrees colder. Diving in with a running start, a swimmer plunges from the warm layer into the cold one, and the body reacts with a cramp.

This is one of the real causes of August drownings: something peasants didn't know in scientific terms but understood perfectly well from experience.

Algal Blooms: An Invisible Danger

There's another reason swimming becomes risky in August: blue-green algae, or cyanobacteria. They start multiplying rapidly once the water warms to 17–18°C, and their peak comes right at the end of July and in August.

Cyanobacteria release toxins that, on contact with the skin, and especially if the water is swallowed, cause nausea, vomiting, diarrhoea and headaches. If a pond is covered with a greenish film and smells musty, don't swim in it, even if the water temperature is comfortable.

In Russia, algal blooms are especially common in still and slow-flowing waters: ponds, lakes and reservoirs. Every year, Rospotrebnadzor, Russia's consumer health watchdog, closes some beaches for exactly this reason. In 2025, for example, of nine official bathing areas in the Moscow Region, swimming was allowed at only six: at the others, blue-green algae levels exceeded safe limits.

Why August 2 and Not the 10th or the 15th?

The date seems arbitrary, but there's logic to it. August 2 is the point where several processes coincide: the nights are already noticeably longer, the water is starting to lose heat, algal blooms are gathering pace, and the weather is becoming less stable, with the more frequent thunderstorms and downpours typical of late summer in central Russia.

Peasants didn't measure the temperature with a thermometer or count hours of daylight. But they noticed the main thing: after this date, swimming became uncomfortable and risky more often than before. And since the date coincided with a church feast, the explanation came naturally: the Prophet Elijah must have decreed it.

That said, the link to a specific date is approximate.

In southern Russia, the swimming season continues into September and beyond. And in Siberia and the Urals, the water in small lakes can indeed cool by the end of July. The saying describes central Russia, the very region where most Russian folk weather lore took shape.

Elijah's Day Traditions: Not Just About Water

The swimming ban is the best-known tradition, but far from the only one. Elijah's Day came with a long list of rules:

• Working in the fields was forbidden. It was believed Elijah might punish people with lightning, burning a haystack or striking the ground.

• Pets were kept indoors: evil spirits could supposedly hide in a cat or a dog.

• Windows and doors were shut tight during thunderstorms so that lightning wouldn't fly into the house.

• Bread was baked from the new harvest and shared with neighbours, a sign that the harvest had begun.

• Bratchiny were held: communal village feasts with beer, meat and round dances.

• Getting caught in the rain on Elijah's Day was considered good luck: such rain was believed to bring health for the whole year.

Weather Lore for August 2

Peasant meteorology was observant, though not always accurate. Here are a few signs tied to Elijah's Day:

• No rain on August 2 means six weeks of dry weather.

• Muffled thunder means gentle rain. Ringing thunder means a downpour. Continuous thunder means hail.

• Heat on Elijah's Day means a long, cold winter.

• Swarming mosquitoes mean clear weather.

• The weather on August 2 will be the same as on the Exaltation of the Cross (September 27).

How reliable these observations are today is an open question. The climate is changing, and "grandmother's weather signs" fail more and more often. But as a historical snapshot of peasants' attention to nature, they're still fascinating.

So, Should You Swim or Not?

Superstition: no. Observation of nature: yes. The ban on swimming after Elijah's Day isn't magic but practical advice woven into tradition, and it worked in central Russia for centuries.

The water really does start cooling in early August, ponds bloom, the weather becomes unstable, and the temperature gap between the surface and the depths makes swimming riskier.

That doesn't mean you have to pack your swimsuit away on August 3. But it's worth taking a good look at the water you're about to step into. No green film, no musty smell, the water still warm and the day sunny: go ahead and swim. But if the pond has turned green and a cold wind is rippling the surface in the morning, maybe the Prophet Elijah really did know something.