biosensor <a href="https://en.wikipedia.org/wiki/ecoSCOPE" class="extiw" title="en:ecoSCOPE">en:ecoSCOPE</a>  with glasseels migrating from the entrance in the middle to the 12 exits at the corners from where water from different sources enters, some polluted -
<a href="https://en.wikipedia.org/wiki/User:Kils" class="extiw" title="wikipedia:User:Kils">Kils</a> at <a href="https://en.wikipedia.org/wiki/" class="extiw" title="wikipedia:">English Wikipedia</a>
CC BY-SA 3.0
photo <a href="https://en.wikipedia.org/wiki/User:Kils" class="extiw" title="en:User:Kils">Uwe Kils</a>