Forty-four supporters of the Rotterdam club will, however, still face charges for fighting with Italian police ahead of a Europa League clash with home club AS Roma, said Jeichien de Graaf.
"We aren't able to accurately identify those responsible for damaging the fountain and we don't have evidence," she told AFP.
Intoxicated Feyenoord fans trashed part of the Italian capital in February ahead of the game, including damaging Rome's famous Barcaccia fountain.
The Rome city council estimated damage done to the tourist attraction, which had recently been restored, at more than one million euros ($1.1 million) .
The fans are facing a Dutch judge for "disturbing public order" and one fan also faces an attempted homicide charge for throwing fireworks at the police, injuring one officer.
Their trial is set to take place in Rotterdam in late November and early December.
Sixteen other officers were also injured in the running battle between supporters and police.
Apart from scratches and other damage, the Barcaccia fountain also had to be cleaned of empty beer bottles and cans, causing outrage among Rome's citizens.
Dutch Prime Minister Mark Rutte afterwards apologised to his Italian counterpart Matteo Renzi.
The match ended in a 1-1 draw with Roma going through after winning the second leg 2-1 in Rotterdam.