When these things first appeared in the NOP, I wondered what they were. A few weeks later it was finally in the papers: every time you see one of these poles, it means a ship wreck was found close to it. Most of these wreck poles were found around the former island of Schokland. When Schokland was still an island, Lake IJssel was the Zuiderzee, or an inland sea. The weather could get really rough and many ships barely made it back to port.