Help - newts are dying!

I use the water-butt on my site to water my plants and had been told that there are lots of newts quietly living in it. I've never disturbed them and haven't come across any until... the Council cut the grass back on the site for the first time since I've had my plot and a thick layer of grass has covered the top and 100s of newts are lying on the top looking extremely ill...
 :cry:
I removed most of the grass with a hand-fork and got some fresh water in (it automatically re-fills from a tap as you remove water) and some seemed a little happier...but for about a hour or so they seemed unable to move and completely unable to repond to me moving the grass around them...and possibly many are dead...
Has anyone got any ideas about why? Could the grass deoxygenate or warm up the water? Produce a toxin?
Those that did revive gasped at the sides - should I make a newt-ladder?  
I've notified the Council and they've said they'll take steps to avoid a reoccurrence; but if people don't know they have newts this could, I suppose, be happening to waterbutts in sites everywhere...!

a newt ladder may not be a bad idea either, if you have a rock large enough to go on the side of a pond it is meant to help newts and frogs get in and out of slippery man made sides. So the same idea could apply, I don't know how you would do it though! :?

 We found 3  newts in our back garden in the past few weeks, and we don't even have a pond they were all hiding under paving slabs. We took them next door to neighbours pond, they all seemed to go into some sort of shock (defence?) and were completely still while the kids all looked at them I sat them on the side of next doors pond, one shot in happily, but the 2 others just froze and sat there being lapped by the pond one even got floated away on the surface I kept and eye, and after an hour one was still there but 5 mins later gone, so  I think they just sit and wait.