I could be wrong, but I think it highly unlikely that it be crows that are causing the toads to physiologically react in this way in such great numbers. Apparently they have been seen moving around, swelling up and then exploding. Crows can cause toads to explode by pecking on them for their livers but this is something thats already supposedly true and known, even if the toads are exploding in unusually high numbers. If this is what the fuss is about then thats what people should say.
I am more inclined to go for the virus/fungus theory (purely because its more interesting and its more fitting to the number of exploding toads, otherwise a shedload of crows have a lot to answer for). Even though tests have shown that the levels of possible pathogens in the water are negative, it doesn't mean that these tests are right as they could be there but in very minute quantities and that it only takes, say, one or a few of the viral/fungal cells to cause this reaction. The idea of it being a virus also makes more sense as viral cells can multiply within a host far more rapidly than fungal cells, therefore, causing more damage at a far more rapid rate. The only ways in which the fungal cells could cause damage just as quickly was if they were spores or released a potent toxin.
Well I think I've tore this to shreds enough and this is just my opinion. I may well be proved wrong but then I'm not perfect and not always right because if I were, I wouldnt need educating would I?