They are called Blässhüner (pale chickens) in German and are a member of the Rail family. They pick along the grass for tidbits like chickens but are also great swimmers and divers. It looked to me like they were eating fresh water clams when they could find them. Seeing them on land shows their curiously chicken-like feet.
They are also known to be feisty, aggressive birds when it comes to territory. I often saw one chasing another long distances through the lake. Occasionally the other bird put up a fight which I captured in this little series. It looked like they were going to fight to the death. It went on quite a while! You can see how the feet come in handy in a fight! I fooled around with the lighting in a couple of these and put them in here just for fun. Quite dramatic, I thought.