To add to Liz's post, the incident was first noticed/started late on Saturday, with sewage or something similar coming into the Teifi along a sidestream a bit downstream of the Lampeter road bridge, near Abercoed. Lots of dead fish noticed, including large sea trout & salmon, but also plenty of small fish, even frogs.
NRW staff were walking the banks on Monday to assess the extent of the effects - but river discoloration was apparently seen as far down as Llandysul. I don't know how far down dead fish were seen.
In terms of direct, immediate effects on birds there probably isn't much, but of course this type of pollution has profound and quite long term effects on river ecology. Perhaps the only slightly good news is that as this incident occurred downstream of Tregaron Cors Caron and the good wildfowl areas from Pont Einon and Pont Goch are not affected.
It is worth noting that there will not be a lot of detail in terms of causes/culprits from NRW for the understandable reason that it might result in later prosecution(s).