Why is April 30th a major holiday in Vietnam? Because it's Reunification Day, when in 1975 the North Vietnamese, commonly known as the "Viet Cong," captured the capital, Saigon, which at that time was ruled by an American puppet government.
And why is May 1st a major holiday? Because it's Labor Day, and the country is socialist (after all).
Unsurprisingly, during these days Ha Long hosts the so-called Ha Long Tourism Carnaval Festival, basically a Brazilian-style carnival. The event is serious and colorful, broadcast in prime time on TV, the whole nine yards. We saw a rehearsal during the day, a bit closer to the evening. Anyone who has seen the pretty good cartoon "Rio" doesn't need an explanation.