Carved into the top are the words "Höchste Hochwasser", which Google Translate says is "Highest Flood". This must be a marker showing the highest recorded water levels of Lake Constance in Bregenz, Austria. <a href="https://en.wikipedia.org/wiki/en:Lake_Constance#Recent_floods" class="extiw" title="w:en:Lake Constance">Wikipedia</a> lists the 1999 event, as well as a more recent flood in 2005 which saw waters rise by more than 70 cm in a few days.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/50811886@N00">warrenski</a> from Cape Town, South Africa
<p><a rel="nofollow" class="external text" href="https://www.flickr.com/photos/warrenski/3005278221/">Höchste Hochwasser</a>
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<ul><li>Uploaded by <a href="//commons.wikimedia.org/wiki/User:Aa1bb2cc3dd4ee5" class="mw-redirect" title="User:Aa1bb2cc3dd4ee5">Aa1bb2cc3dd4ee5</a></li></ul>