There are now very real fears the Dam will fail and collapse, sending massive amounts of flood waters downstream, killing millions and wiping out all manufacturing in China.

The satellite images below tell the story better than words.  The photo on the left is the Dam, right now.  The photo on the right was how the Dam looked before the flooding.

The amount of compression deformity is stunning.   This is not a piece of plastic or steel that can readily bend; this is concrete.   

While concrete has terrific compression strength, and can handle enormous downward weight, it has very little tensile strength.

Ultimate tensile strength, often shortened to tensile strength, ultimate strength, or within equations, is the maximum stress that a material can withstand while being stretched or pulled before breaking.  

That's why engineers use very high grade steel reinforcing when building something like a Dam.  The steel prevents the movement of concrete from stretching or bending.   It looks now, however, that either the Chinese engineers didn't use the right steel, or perhaps didn't use enough steel.