User blog comment:Peter Griffen Boy/Swimming/@comment-1407184-20100704154259

They did it mainly to stop you from accessing parts of the map in Single Player that you aren't supposed to until a certain point. Right when you start the game, you will notice there are no open bridges to West Elizabeth, and no open bridges to Mexico. And, in Multiplayer, the had to do the same thing, or people would say "Why can I do that in Multiplayer, but not in Single Player". And, why use water to block points? Well, using mountains everywhere would be pretty ridiculous, and then explain how you can get past them later? It's really the only way that works. I will say, though, that standing neck deep in water and being fine, then taking one step and dropping dead, is pretty ridiculous.