CorSec Engineering have released a River pattern gaming mat.
From their announcement:
We have added a new river pattern the the store. This mat is scaled to work with 6mm but can easily be used for 15mm. Like all our mats it will be printed on high quality cotton. They are available in 108″ by 58″ This one was created with high resolution satellite images and is available with a wide range of hex and square overlays.