http://www.livius.org/ga-gh/germania/drusiana.html
"The Fossa Drusiana was the canal between the rivers Rhine and IJssel, dug by Roman soldiers at the end of the first century BCE. The project was probably in some way connected to the mole at Carvium. The canal still exists as the upper course of the IJssel; two radiocarbon-dates from the oldest deposits of this river suggest that they date back to the beginning of our era... A more recent interpretation points to the fact that the ancient sources speak about the canals of Drusus, and suggests that a second canal connected Lake Flevo with the Wadden Sea."
Thank goodness! ...and none too soon!