Heat waves and low rainfall over the past couple of months has brought Poland's Vistula River to its lowest level since records began 200 years ago.
Now, police are teaming up with archaeologists to recover the huge cargo of marble treasures that have been revealed.
Researchers say they were aware of the artifacts dating back to the mid-17th century, but low water levels have helped uncover what was beneath the riverbed.
On Thursday, a police helicopter lifted ornaments and stonework, which was believed to be looted from Warsaw by Swedish invaders.
"This is a precious find," said Marek Wrede, a historian at the Royal Castle. "These elements were stolen from Warsaw's royal residences and palaces."
Newly retrieved objects include marble tiles, parts of archways and columns. The centrepiece of a fountain with water outlets was discovered as well.
According to historians, the material will provide more evidence about what happened four centuries ago.
It has not yet been decided where and when the items will be publicly displayed, but some of the stonework is currently being stored at a building owned by the Warsaw river police.
With files from The Associated Press