Unfortunately, the image resolution is not good enough to make a morphological description, so it is very hard to determine whether it is diatoms, dinoflagellates, cyanobacteria, chlorophyta, etc.
It looks like a chain-forming colony. Is it right? Or are they solitary cells (not forming any colony)
Are each cells connected to each others via thread-like structures (either single, or many threads)?
Is the cells looks like it has thick cell wall?
Assuming it belongs to diatom group, the rounded cell and (presumably) chain-colony connected by thread/s, it might be Thalassiosira spp.
But much detailed morphological description could only be possible if you have better resolution image or using electron microscope.