Question of Commentarri de Bello Gallico

Dear all,

This below sentence is extractet from Commentarri de Bello Gallico - in the section of Conspiracy of Orgetorix:

… ūnā ex parte flūmine Rhēno lātissimō atque altissimō, QUI agrum Helvētium ā Germānīs divīdit

I have referred to a translation from website [http://www.forumromanum.org/literature/caesar/gallic_e1.html#2]

… on one side by the Rhine, a very broad and deep river, which separates the Helvetian territory from the Germans

That seems that the demonstrative Pronoun QUI refers to flumine, but QUI is Mas and flumine is Neu. It must be QUOD that agrees with a Neu noun, mustn’t it?

Sincerely yours,

It refers to Rhenus, which is masculine.

@ Tertius Robertus: Thanks so much