A combination of unusually warm spring weather and spawning frogs that stirred up the mud and so released a lot of of nutrients into the water recently led to an algal bloom in our garden pond. Large patches of algae floated on the surface in mucilaginous mats that trapped bubbles of oxygen.
Under the microscope, at x40 magnification, the algal cells were round, highly motile and present in vast numbers. This group represents the population in about 2% of a single drop of water.
The same, but at x100 .... and at ....
.... x400. I am not certain what species this is but I think it may be Chlamydomonas. The paired flagella of each cell are not resolvable with this microscope at this magnification.
The most striking aspect of this algal bloom, apart from the sheer numbers of cells, is the hyperactivity of the algae. The bubbles of scum on the pond surface may seem static, but at this magnification they represent a surface film of frantic activity.