The photo was taken on the 10th of January; the lake was drained the day before (or perhaps the day before that, I wasn't paying that much attention). The sluice gates are still open as I write - surely this can't be intentional?
I've been corrected in my assumption that Caradon have something to do with draining the lake - it's the Environment Agency. If it's not refilled soon we'll be losing some of the wildfowl which prefer deeper and non-tidal, non-saline water. A cause for concern.
Time to contact the Environment wallahs and ask what's going on.