James Nolan went missing Sunday in Bydgoszcz and his corpse was discovered Wednesday by police divers. His death was likely an accident since there were no external or internal injuries that could suggest foul play, prosecutor Wlodzimierz Marszalkowski told The Associated Press.
"There is no other hypothesis than an accident," Marszalkowski said. "There are no doubts, no circumstances to suggest otherwise."
Prosecutors will nevertheless continue to check security camera footage in an effort to clarify the circumstances of the drowning.
Nolan, 21, of Blessington, County Wicklow, was in Poland with friends for the European Championship to follow Ireland, which has now been eliminated from the tournament.
Several of Nolan's relatives placed candles along a canal where Nolan's body was found. They also held a news conference at which they thanked city authorities for the efforts made to find Nolan.
The news station TVN24 showed several family members crouching under umbrellas as they lit a candle in rain and placed a bouquet of flowers on the water's edge, one women putting her arm around a man in consolation.
The news agency PAP quoted his uncle, Patrick Nolan, in expressing relief at the finding that there was no foul play involved in the death. He also said the family was touched at the help and support shown to them by the city, where authorities carried out an extensive search for Nolan.