The 505 participants each swam the course of 25 metres (27 yards) marked out in a former submarine dockyard, taking 4 hours and 50 minutes to do so.
The swimmers, many attired with funny hats, ranged from a 9-year old boy to an 83-year old woman, and included a pregnant woman who joked her effort should be counted for two.
"It's actually a smart thing to do at this moment”, Roy Vissers, one of the swimmers, said after emerging from the 4 Celsius (39.2 Fahrenheit) waters into the below-freezing air.
He believed the sport provided good protection against COVID-19.
Dozens of spectators cheered along the course, many from hot tubs and mobile saunas set up along the side.
Aivar Tugedam, a winter swimming enthusiast who organized the event, said he had seen the sport grow in popularity since Estonia first went into a coronavirus lockdown in spring.
“Let's say from spring until now, I would say the count of the winter swimmers have tripled in Estonia. It's gone wild and really popular”, he said.