That will be because the bridge sections have a tiny health radius.
Impacts inside the red circles will do 100% damage, outside this radius it will fall off exponentially.
![screen shot 2014-01-03 at 11 52 59](https://f.cloud.github.com/assets/167819/1836284/127c637c-7401-11e3-951d-621b5ed8cf1c.png)

The red circles in the water are caused by the bogus bridge setup in battle lake.