Well, here are the basics:

1, if you want an uncrossable water you have to make a river that crosses the entire map.

2, if you have a river like that then the other water surfaces will be uncrossable too (if i remember correctly)

3, it follows from the previous points that isolated lakes can be always crossed (if there is no proper river or ocean in the map).

4, there can be only 3 bridges in any given map.

5, a bridge will run through the entire map, thus will cross any water surface in it's way.

6, bridge can be made only through an uncrossable water, i.e. you cannot make bridges across isolated lakes.

have fun: Cheetah

[This message has been edited by Cheetah (edited 05-28-2002).]