This is arrowhead (Sagittaria sagittifolia), pijlkruid in Dutch. It is a native plant in most of Europe.
The leaves seem to indicate where to go, but unfortunately they all point in different directions.
Olympus Stylus 1s, 300mm, ISO200, f5.6, 1/125s
"The round tuber is edible. It tastes bland, with a starchy texture, similar to a potato but somewhat crunchier, even when cooked." (Wikipedia)
It is also nice to look at.