Protesters carried a wide variety of banners (see pictures) comparing EU President Jean-Claude Juncker to Hitler and Stalin and demanding the resignation of the government.
Saeima deputies Janis Dombrava and Inguna Ribene were among the marchers who followed a short route from the Occupation Museum to Freedom Monument.
"I'm in favour of border controls. The refugees are not victims, most of them are here for money," protestor Pols Vaivods told LSM as he displayed a banner praising Hungary and its Prime Minister Viktor Orban.
"We should be helping Hungary - we are brother nations," he added.
"This is not racist. We are against taking in refugees but we can help them in other ways, maybe by sending medical aid," suggested protester Ainis Pogris.
Some demonstrators told LSM they were against all immigration, others that they were not against taking in refugees from countries such as Ukraine.
Tourists looking at the demonstration as they took in the sights of the Blackheads House and Town Hall were generally puzzled.
"I don't think it's fair. We are expecting 800,000 refugees this year so Latvia should do its part too," said German tourist Khristina Gerhen from Riga's twin city of Bremen.
Frenchman Roger Ravel from Lyon said the demonstration reminded him of Front National events in his homeland.
"It's surprising to see it here, but countries really need to think whether they want to be part of the European Union or not," Ravel said.
At the Freedom Monument, the crowd listened to a concert of patriotically-themed songs before dispersing.