The little red plant in the middle of this pond glop is called mosquito fern, Azolla caroliniana. It is a true fern and the only aquatic one we have.
The other plants with the little leaves are various species of duckweed -- I'll have to devote a whole post to those one of these days. The barely submerged, darker green gunk is some type of algae.
Our hot, dry June has left us with more algae than we like to see this time of year. As it dies and begins to decay, the algae will take up a good bit of the dissolved oxygen in the water. What we need is a nice soaking rain that will cause the pond to rise and move some of the floating mats of algae out and areate the pond at the same time.