Went down to the river (Kaw/Kansas River) today and grabbed a sample that consisted mostly of a rock covered in slippery algae. I was kind of amazed to see it under the microscope - there was so much activity and diversity.
What you’re looking at here are mostly diatoms, which are unicellular photoplankton and are considered algae. Colonies of them typically look like brown, slippery slime on rocks and sticks in stream waters. An interesting feature of diatoms is that their cell wall is made of silica, and when they die that silica skeleton can become diatomite, or diatomaceous earth.