According to History.com:

“On April 20, 1980, the Castro regime announce[d] that all Cubans wishing to emigrate to the U.S. [were] free to board boats at the port of Mariel west of Havana, launching the Mariel Boatlift…

“In all, 125,000 Cubans fled to U.S. shores in about 1,700 boats, creating large waves of people that overwhelmed the U.S. Coast guard. Cuban guards had packed boat after boat, without considering safety, making some of the overcrowded boats barely seaworthy.”

The Politico’s Andrew Glass reports, “Most of the Mariel refugees decided to live in Miami, increasing by 20 percent that city’s Cuban working population. Washington and Havana agreed the impromptu exodus would end Oct. 31, 1980.”