The picture was taken in summertime. As this stream is perennial, the water level decreases significantly during the summer. 
A Nature and Parks Authority employee at the site said that the water was diverged from another source (as normally it would be dry in the summer).
<a href="//commons.wikimedia.org/wiki/User:Hexafluoride" title="User:Hexafluoride">Hexafluoride</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>