One man was arrested after scaling the boundary of Leinster House when tensions flared briefly but the Dublin march was peaceful and good-humoured - though designed to inflict maximum disruption to traffic on both sides of the Liffey.
In Cork an estimated 4,000 people protested to highlight their ongoing opposition to water charges.
The Leeside protest was organised by an alliance of a dozen anti-water charge protest groups, brought the city centre to a standstill as demonstrators marched from the Grand Parade up Patrick Street.
The People Before Profit TD Richard Boyd Barrett said those who were hoping that unrest over water charges would subside over the course of time were mistaken.
"The friends of the Government, in various quarters, have been hoping and wishing that the massive popular rebellion against water charges and the wider austerity agenda would end - they are sorely mistaken," he said.
At least three separate Dublin marches converged on O'Connell Street.
The first group of 6,000 mainly protestors from Dublin's northside marched from Connolly Station and up the south quays. A smaller feeder march from St Stephen's Green joined this main grouping at O'Connell Bridge.
At the same time another march, mainly from the southside, were walking down from Heuston Station on the north quays. The two groups exchanged greetings as they marched past each other on opposite sides of Capel Street Bridge.
Luas services were suspended, bus services disrupted and there were tailbacks all around the city - though gardai successfully implemented diversions to ease some of the traffic chaos.
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