For context, see [[2940080]], where this object is visible out in the water beyond the valve tower. The manufacturer's blurb for this object describes it as a "potable water storage mixer". It mixes the water from the surface, rather than, as is often the case, from the bed of the reservoir; the resulting circulation helps to maintain water quality.
Uploaded to Geograph by Lairich Rig on 9 May 2016
Photo © Lairich Rig, 9 May 2016. Licensed for reuse under this Creative Commons licence