Yllek Nishi

I have 2 parcels which are intersected by a Linden River. I would like to build a bridge over the linden river so that I can connect my 2 parcels together. Are there any rules that I have to follow (i.e.. Do I have to have the bridge at a specific height above the water level) or is there a rule that says I simple cannot Do this ? Any help / advice appreciated. Wylye Nishi