We had a spill on the Colne a few years ago, while I was fishing. The stretch I was on had a weir at the top, and ran parallel to a road. The first I knew of it was just as dusk was drawing in, when what looked like dozens of icebergs the size of a car were drifting down the river towards me
I followed them up, and on reaching the weir I found that the whole structure had disappeared under an off-white mountain, and parts of this were being blown by the wind across the road, causing a visibility hazard there. Obviously it was foam of some sort, being stirred up by the motion of the weir...it covered the weir the whole width of the river to a depth of several feet, with the iceberg like lumps breaking off at the tail, to drift away.
I 'phoned up the EA, who didn't bother coming down, but relentless pursuit on my part resulted in the information that 'An amount of industrial detergent had been released into the surface water drainage system upstream of my position, but they had been unable to identify the source'. I could find no further details later, and as I was unable to get back to the river for some time, I never did find out if any fish deaths or whatever resulted from this... the EA were keeping schtum, and nothing appeared in the local press.
Undoubtedly, damage was done, but I guess it was consigned to the 'Hey ho, never mind' bin
Cheers, Dave.