He was a member of the Finland football team which played at the 1912 Summer Olympics in Stockholm, losing 4–0 to England in the semi-final.
Over the years, he used various tricks to dodge police boats – and sometimes the bullets of their machine guns – during his trips between Turku, Helsinki, Tallinn and Stockholm and in the Åland archipelago.
In one case, he unloaded his cargo right in the heart of Helsinki while people were distracted during the visit of Gustav V of Sweden.
In 1938, prior to World War II, Niska began to smuggle something else – Jewish refugees from Germany to the relative neutrality of Finland.
He used stolen and forged passports and various devious plots to get Jews from Germany through the Netherlands and Estonia.
In the mid-1940s, Niska tried to finance the building of a new boat by giving interviews about his life – he needed the money and knew he could afford to ask.
He wrote two books, Yli vihreän rajan (Over the green border) and Mina äventyr (My adventures).