Looks like you do have rivers in VizWorld, but it's sitting behind the region... ideally you'd separate the rivers then place it back on top of the region. There's no easy way as far as I know... perhaps create a new client above the region and use a TPL that has *just* rivers on.
You can't use two TPLs in the same client, but perhaps if you separated them into two layers/clients and edit them separately? Not particularly neat, though.
On the CMWClient plugin that is creating the regions you can enable under the 3D Objects tab > Advanced the option Copy Map to Region, this will copy the texture from the TPL (including lakes and rivers) on top of the selected region