In Moscow, the police detained two young people walking with balloons. OVD-Info was told about this by the activist of Navalny's campaign headquarters, Nikolai Kasyan.
The detainees are in the Kitai-Gorod police department. What they are charged with is unknown.
UPD. 19:57 Nikolai Kasyan tweeted that all the detained volunteers were released, they were issued protocols for violating the rules for participating in a mass rally (part 5 of article 20.2 of the Code of Administrative Offenses).