Diatoms are brown microalgae that can be found in all freshwater and marine environments. They are an important link in the ecological cycle. In streams and rivers you often see stones covered with a brown layer that is formed by diatoms.

Green masses in ditches and ponds are often caused by networks of long threads originating from filamentous algae.

Cyanobacteria or blue-green algae are undoubtedly the most important microorganisms that have ever appeared on Earth. Here you can read more about these fascinating microorganisms.