What on earth is in my pond?!

For a while the pond water was amazingly clear. Suddenly it's got cloudier, and when I looked in today there are thousands of tiny spherical creatures swirling around. I got a clear bucket and scooped some out to try to get a photo.

Please click on the image as the full-sized version is better.

I also took some underwater footage in case that was any clearer. There seem to be larger black dots in some of the objects - more developed?

Other, slightly poorer footage

Anyone have any ideas?!?

A closed mouth gathers no foot.