It is a sure sign summer has come to Moscow when it starts snowing. Only in summer it snows white fluff.
For around three weeks in June and July the female Balsam Poplar tree sheds its seeds.
Moscow's streets in June and July are filled with whirlpools of fluff
Every street in the city is filled with whirlpools of fluff; drivers have to wipe it from their windscreens; pedestrians are forever picking it out of their eyes and noses.
In the sticky heat of summer, an entire white beard of fluff - or pukh - can attach itself to you in one short walk.
In the gardens next to the Kremlin, visitors to an outdoor cafe have an extra seasonal garnish to contend with.
"We just eat our ice cream with the fluff in it. You can't spit it out after all!" one woman shrugs.
But further up the path, Valentina's having trouble selling her hot dogs.
"The pukh really gets in the way," she complains. "Nobody wants to buy my sausages with fluff all over them. And it makes my nose itch."
There are urban myths galore about the trees. Some say they were Nikita Khrushchev's favourite so he ordered them planted en masse in the capital. Others call the fluff Lenin's snow.
Whatever the truth, the Balsam poplar now lines most roads here; they are crammed into every city yard.
"It's the female poplar that gives off the pukh," Alexandra explains, her nose twitching in alarm as another white clump floats past, in the yard of her apartment block.
"The problem is when we planted the trees we just wanted it to be green quickly - and we didn't check!"
City gardeners know better now, and avoid the Balsam Poplar altogether.
But across town at the department responsible for Moscow's greenery Gennady Zubkov says they are powerless against the thousands that already exist.
"The only way to fight the fluff is to prune the poplars every couple of years. But there are so many in Moscow we just don't have the money!" he explains.
Female poplars which shed the white fluff, known as pukh
"Anyway we can't spend all our cash battling pukh. We have lawns to look after too, and flower beds."
Meanwhile the pukh wreaks havoc with hay fever sufferers, as it picks up pollen as it flies.
Others accuse the fluff of worse.
Christopher is an expat businessman in Moscow, who has fallen ill here every summer. His doctor is convinced it is because of the pukh.
"Every time I've been here in summer, I've got this enormous swollen throat, that feels like there's glass and ground nails in it," Christopher complains between sneezes. "Just walking through Moscow at this time of year is about as pleasant as walking through a haze of insects!"
According to Gennady Zubkov there will be no respite until the trees reach the end of their natural life - in several decades time.
In the meantime, after a particularly fluffy start to the season, nature is providing its own temporary solution.
Torrential rain storms are helping keep the pukh down this week - safely away from the city's irritated nostrils.