The sea stone, which is the weakness of devil fruit users, was said to have the same power as the ocean, and it was said that the sea rejected the devil fruit users. I understand that devil fruit users can't swim, but if they were standing in a river or fresh water of any sort, would they still lose all their strength and be unable to do anything? I tried to search for it, but they closed it and archived it, so can anyone help please?
According to wiki there is a nice explanation about weakness of Devil fruit. I would like to highlight few points which might help you.
Oda stated in an SBS that Devil Fruit users are susceptible to all types of water, not just seawater.
This includes the white sea surrounding Skypiea. He elaborated on this, saying that "moving" water, like rain or waves, does not weaken Devil Fruit users, while standing water does. This was also shown first when Monkey D. Luffy was in the Dance-Powder induced rain and did not feel his power slipping away, and again when on Zou, the sea water that Zunisha used to shower did not affect him despite being sea water as it was "moving" water.
So the main conclusion which is given in wiki that:
Devil Fruit user will not be restricted in the water if he or she is not physically touching the water.
So according to me it might affect as long as devil fruit users are physically touching them.