A hole in the ice which was covering part of the lake in Zell am See, Salzburg (state), Austria, on that day. Holes like this are developing because of gas coming out of the lake ground.
<a href="//commons.wikimedia.org/wiki/User:Wald1siedel" title="User:Wald1siedel">Wald1siedel</a>
<span class="int-own-work" lang="en">Own work</span>