Recently, after a heat wave where we are in Australia, blue green algal blooms affected the river system from which we receive our water. Our 8ML dam (from which is pumped water for sheep troughs) was also affected. After some research we treated it with hydrogen peroxide (50%) at a rate of 100L for the 8ML. We sprayed it in from a boat, using a hose with a nozzle and 'mixed' it by speeding the boat around the dam.
A day later and the water has turned a bluish opaque colour.
I understand that the hydrogen peroxide has probably destroyed the cynobacterial walls, hence the colour. My question is will this release toxins into the water (that we should be worried about the sheep drinking)? or does the hydrogen peroxide also destroy the toxins??

This is a UK site so its unlikely we will have direct experience of this. from my reading of the scientific literature the hydrogen peroxide will definitely release the cellular contents and measurements of those MC toxins can rise over 10 fold. There is no reason to think the H2O2 will destroy these toxins. see … getps6ptEg