By Lucy Papachristou

LONDON (Reuters) - Last August, a middle-aged Russian woman with her face covered walked onto Red Square in Moscow and, in the shadow of the Kremlin, scattered handfuls of coloured rubber balls on the cobblestones below.

Scrawled on the balls in pencil were slogans: "Freedom for political prisoners", "For our and your freedom" and "Hi, it's Navalny" - the last one the well-known catchphrase of Alexei Navalny, Russia's most famous opposition politician who died mysteriously in an Arctic penal colony one year ago on Sunday.

Two weeks later, authorities arrested another activist, Vera Novikova, who they said had filmed the stunt. She was fined 20,000 roubles ($200) and jailed for 15 days for displaying "extremist symbols", according to Moscow's courts service.

Through her lawyer, Novikova declined to speak with Reuters.

The Kremlin could not be reached for comment. While Navalny was alive, Moscow cast him and his followers as Western-backed troublemakers intent on sowing chaos in Russia and destabilising it from within.

The woman who conducted the rubber ball protest said she was moved to act by the memory of Navalny and to honour a 1968 protest by Soviet dissidents on Red Square against the invasion of Czechoslovakia.

"I wanted to inspire supporters of change," said the woman, who asked that her name be withheld for her safety. Soon after the stunt, fearing arrest, she fled Russia for a European country, saying she did not want to live in a "dictatorship".

In the year since Navalny died suddenly aged 47, dozens of Russians are still being arrested, tried and imprisoned for engaging in activities related to him and his memory.

In Russia, where the politician was serving more than 30 years behind bars for extremism and other convictions, even to display the word "Navalny" risks a jail sentence, as Novikova discovered. This month a court in St Petersburg ruled that to publicly show his photograph is to endorse extremism.

Russian rights group OVD-Info has tracked 695 detentions relating to support for Navalny since his death last February 16, said Dmitrii Anisimov, the group's spokesperson.

OPPOSITION IN EXILE

The majority of those detentions - 442 - occurred at makeshift memorials to the politician in the days immediately following his death. Nearly one hundred people were arrested at Navalny's funeral in Moscow, where a crowd of thousands marched to the cemetery chanting his name.

Since mid-March, as mass mourning events waned, OVD-Info registered 35 Navalny-related detentions, including Novikova's.

"The number (of detentions since mid-March) is relatively small, though still significant," Anisimov said. "Rather than mass detentions, pressure on Navalny's supporters after his death has mostly taken the form of criminal prosecution."

Since Navalny died, 21 people have faced criminal charges for associating with him, Anisimov said, including three of Navalny's lawyers who were jailed for 3-1/2 to 5-1/2 years for "extremist" activity.

The continued crackdown on Navalny supporters demonstrates the Kremlin's determination to stamp out any criticism as the conflict in Ukraine approaches its third anniversary.

The aim is to erode Navalny's "potency as a threat to Putin," said Ben Noble, associate fellow at Chatham House in London.

But in the year since his death, the often bitterly divided and scattered Russian opposition groups working from exile have struggled to stay relevant to Russians who remain in the country, Noble added.

For the Kremlin, high inflation caused by heavy military spending "presents a much stronger challenge right now than the political opposition abroad," he said.

Nevertheless, authorities' crackdown on activists aligned with Navalny has a chilling effect on others who might want to protest, said Russian political scientist Ekaterina Schulmann.

"This is intended to send the self-evident signal to the others: don't meddle," she said.

POLITICS WITHOUT FEAR

A lawyer by profession, Navalny pronounced Putin's United Russia a "party of crooks and thieves" and said he would fight to the end to see "the beautiful Russia of the future".

Western leaders, Navalny's allies and his widow, Yulia Navalnaya, accused the Kremlin of having him killed, which Russia denies. U.S. intelligence agencies later determined Putin likely did not order his death.

From Vilnius, the Lithuanian capital, the watchdog Anti-Corruption Foundation (ACF) Navalny founded in 2011 continues to publish investigations into alleged graft among Russian elites.

For ordinary Russians, assisting in this work can be costly.

The Nobel prize-winning rights group Memorial says at least 14 people have been criminally charged for donating money to the ACF - a U.S.-registered nonprofit labelled a "foreign agent" and an "extremist" group by Russia. A guilty verdict can bring up to eight years in prison.

Konstantin Kotov, a computer programmer and human rights advocate in Moscow, was facing prosecution late last year for six donations of 500 roubles (about $5) each to ACF dating back years.

No stranger to protest, Kotov served time in prison five years ago for helping organise mass rallies, and has been arrested and fined several times since for demonstrating against the war in Ukraine, among other activities.

"Navalny showed all of us Russians an example of what it means to engage in real politics, to engage in them to the end, without fear of any consequences," he told Reuters.

Last month, while under house arrest awaiting trial, Kotov decided to make a run for it, taking advantage of the faulty technology of his court-ordered ankle bracelet tracker. He is now in Lithuania and considers himself lucky. But others still in Russia might struggle to leave, he said.

"If a person has no documents, no one is waiting for him abroad, what will he do?"

(Reporting and writing by Lucy Papachristou; Editing by Mike Collett-White and Ros Russell)