Kubkowski set off from Sweden on Friday and reached the beach at Dziwnów, on Poland's north-west coast, at around 8 p.m. local time on Sunday, where crowds of supporters had gathered to greet him.
According to his support team, Kubkowski swam continuously for the full 55 hours without resting, sleeping or touching the accompanying boat – the first person to complete the crossing this way.
Half an hour before the finish, he stopped to rehydrate and change the swimming cap.
It was his fifth attempt and the first to succeed.
Speaking shortly after emerging from the water, Kubkowski said he was too exhausted to describe how it felt.
Team member Marcin Cieślak said crises are unavoidable in such a challenge, particularly those caused by sleep deprivation.
By the second night without sleep, he explained, toxins build up in the brain and hallucinations often follow – and it was these that caused Kubkowski to "lose consciousness and touch with reality" at points during the swim.
He credited diet, training and preparation with keeping such episodes to a minimum.
Kubkowski first attempted the crossing in 2022, when he swam 115km in 32 hours.
He came closest to success last year, covering 159km over 53 hours before the attempt was called off after he lost consciousness, just 11km short of the finish.
He dedicated this year's successful crossing to children supported by the Cancer Fighters Foundation, which was raising funds during the swim.
Kubkowski holds the world record for 24-hour swimming and is a multiple Polish and world championship medallist.
He is also the founder of the Ultra Baltic Swim project.
He was not the only swimmer attempting the crossing that day.
Karolina Szczepaniak, an Olympic swimmer who competed in Beijing and London and holds the world record for continuous 72-hour swimming, also set off from Sweden on Friday on her second attempt to cross the Baltic.
She was swimming to support the treatment and rehabilitation of 14-year-old Piotr Małolepszy, and aimed to reach Pobierowo.
A few hours after Kubkowski's success, Szczepaniak ended her attempt after 58 hours in the water
"Thank you," she wrote on Instagram, confirming she had ended her bid to swim from Sweden to Poland.
(ał/mk)
Source: PAP