This is growing inside one of the galvanized stock troughs. It's new to me. The others have green algae, but this one only has this white. It is making the water opaque, sort of like if you poured milk into the water. There are goldfish there - or were the last time I got a glimpse of them. The water is too cloudy to see into. I'm in the process of using up the water here so I can clean the trough and start over and when dry it's texture is like chalky powder. I'd think it was mineral buildup, but this is primarily rain water in this trough.
Edited to add that I see no green in this at all. Without any sign of photosynthesis, I'm thinking it may not even be a plant, but something else. The same water is growing green algae in a rubber trough next to this one. No white growth in it.