No idea but it would be as well to notify
www.arc-trust.org which is the reptile and amphibian conservation trust.

Thats sad, has anyone used slug pellets or contaminated the water?

Having the same problem with toads. Had to re do our pond at work due to massive leak so the toads have just come down to spawn. Most of those who died were females so i presume they were just to exhausted from spawning

Thanks all for your comments . I don't use slug pellets or herbicide/insecticide the wild life and birds I very important to me and my garden.