Angry?  Dangerous?

No, just thirsty.

Swallows drink by dipping their beaks in the water as they skim above it.

With perfect timing and a lot of patience, the photographer (sanchezn) captured this bird approaching head on.  His photo won Third Place as Picture of the Year on Wikimedia Commons.

Click on the image to see the original.  It is awesome in larger format!

(photo of a barn swallow, Hirundo rustica, by sanchezn from Wikimedia Commons, CC BY-SA 3.0)