Here's something I've never seen before, a Blue-winged Teal feeding in a ditch full of purple sludge. This was at Terra Nova Park in Richmond BC. The duck seemed happy. What was the sludge?
A look through binoculars showed flocculence flecked with duckweed. The picture isn't sharp-sorry, for some reason I was having trouble with focus today.
But you can sort of see that the purple layer is made up of individual plants that spread on the surface of the water. I believe this is Carolina mosquito fern, Azolla caroliniana, a freshwater aquatic fern, which is neato, but which also is an invasive species native to eastern North America and other places that are not here. It seems invasive foreign species enjoy ditches.