Cyanobacteria (in this case possibly Arthrospira sp.) moves through a process called phototaxis in response to light. Enjoy 3 minutes of peaceful and hypnotic movement, filmed in real time.

Cyanobacteria might look like filamentous algae (and in fact for a long time was referred to as blue-green algae), however thet are prokaryotes, without a nucleus or organelles, while algae are eukaryotes.

Sample from my pondwater microorganism aquarium.