We have the only one bridge, so we decided that rivers can be crossed by everyone. Units must stop at the edge of water, than they must be given another order for movenment further. If some unit is in a river it has -1 order penalty, it is NOT in defended position and rivers do not block LOS.
Any wargame is good only when it is more than 'kill everybody'! We also play Dropzone Commander very frequently. Beautiful tactical game, one of the best!