For a more in depth analysis of water levels and rainfall over recent years see
Analysis of Water Levels and Rainfall at Tring Reservoirs
You will probably know that Tring Reservoirs were built, and are still used, for feeding the Grand Union Canal, being at the highest point. During the summer obviously there is little rain but it is during the summer holiday season when the canal locks are being used regularly that the water levels drop significantly, and rapidly.
Wilstone and Startops(end) Reservoirs are the ones that vary most and give us the mud at more or less the right time for autumn passage waders.
On average there is exposed mud at Wilstone Reservoir from early-August to mid-January, and at Startops Reservoir from end-July to end-November.
We do get wader sightings before there is exposed mud, and these tend to be
Marsworth Reservoir has less variation in water level and normally there is water into the reedbed. This is the prefered habitat for Bitterns which overwinter here.
I have to mention Tringford Reservoir although usually it hardly varies in water level at all. I have included this chart for completeness only.
This constant water level may be great for breeding waterfowl, coots, moorhens and grebes, but we have few records to confirm this.
In 2005 Tringford was virtually drained in the autumn. This was due to new legistlation regarding Blue-Green Algae (which is explained in our Features page). It remains to be seen if this will become the new norm.
