I do have battle mats, which do split the gaming zones via a river (normal water) and also another with acid stream (green poison bubbles). I like the idea, that this terrain can not be crossed but still offer LOS and LOF, but what i di understand from wiki and rulebook (n4) this should be treated as difficult terrain - which seems not fit really. do i did not get it right, or is there any other possibility? thanks
The river would be Difficult Terrain (Aquatic), so troopers without the correct Terrain skill will be forced to stop when entering and slog through it at - 1 movement. N4 doesn't really have dangerous terrain rules yet, I'd be tempted to say treat the acid areas as either impassable or Difficult Terrain (Aquatic) with maybe a low visibility zone above it to represent the fumes. In a casual game you could also make it a Biotechvore zone using the rules from the ITS mission. There aren't really any specific rules for impassable terrain, though I'm not sure it needs anything other than saying "Troopers can't move here."
The rules largely leave terrain to the players. Basically, you and your opponent can make any agreement you want about how to treat the river and the acid stream. I would probably do the same as colbrook - river is just Difficult Terrain (Aquatic), acid is impassable. But you can make it more complicated if you want, and you wouldn't be doing it wrong. Depending on the width of the acid stream, it might make Super Jump have some actual point, which would be nice.