In reality it’s many tiny bacteria that can’t be seen with the naked eye.
Green algae and blue green algae. If you see leaves or roots, or distinguishable parts, it’s likely a tiny (and harmless) aquatic plant like duckweed. Here are a few identifiers: They normally look green and sometimes may turn bluish when scums are.
Web firstly, blue green algae (bga) is not actually algae, but it looks like it. Toxins and/or high cell counts have been. Stringy, silky substances that can be draped over a stick are green algae.