You have probably been to a restaurant that has a decorative guitar on the wall, it’s not playable, it’s just for show? Replica anythings are like that. :^)
Yes, I know what replicas are for, I have some of my own.
However as far as I know replica weapons were not made in Medieval period.
It seems to me that in a time when skilled craftsmen and metals were at a premium wasting time and materials on a purely decorative archaic weapon would be a rarity.
And to find such an artifact in a river would be even more improbable because such a weapon would not be carried.
Certainly art piece weapons were produced.
But such weapons were produced of the finest materials of the day.