That is actually possible, but also dangerous.  On the North Sea side of northern Germany and southern Denmark, and area called northern Friesland, the shallow water stretches for miles into the ocean. The small ferries taking you to the Halligs and small islands have to sail between the sticks marking the path with a little bit deeper water. Sailing with one of these you may suddenly see people strolling in the ocean with their dog. Doing this, however, you have to know all about the tides. Tourists often drown when they don’t manage to reach land in time. Always talk to the locals before wandering in the water, called Wattwandern.