The body was found on Wednesday in the Bug River along the frontier between the two countries, officials told reporters.
The man's identity has been confirmed by another young man with whom the 19-year-old tried to illegally cross the river a day earlier, the Polish state news agency reported, citing a regional police spokesman.
"We also found documents on the body, so there is no doubt that's the 19-year-old Syrian citizen," the spokesman, Andrzej Fijołek, told PAP.
He added that a probe would be launched into the death.
Polish lawmakers last week backed a government plan to build a wall on the country's border with Belarus in a bid to stave off an influx of migrants from the Middle East.
Late last month, the Polish lower house voted overwhelmingly to extend a state of emergency in parts of two regions along the country's eastern border with Belarus by two months amid a growing migrant surge.
The state of emergency gives authorities broader powers to monitor and control the movement of people on the Polish-Belarusian border, which is also the eastern border of the European Union.
The European Commission and Warsaw say the flow of migrants has been orchestrated by Belarus as a form of hybrid warfare designed to put pressure on the European Union over sanctions it imposed on Minsk. Belarus has denied this, the Reuters news agency has reported.
(gs)
Source: PAP, Reuters