How do you get rid of algae in the creek in your backyard?

you cannot. algae may not be pretty, but it means your creek is extremely healthy. if it is in a fishtank, that means you do not need fishfood.

plankton, which is a bacteria that is in water and eats dead things, gets rid of unhealthy substances i.e. unhealthy bacteria.

plankton is healthy for animals to eat. algae forms from clumps of plankton. fish eat algae for food, and when fish naturally die (not from bacteria they eat), plankton eat the body. that is a pond food cycle.

even people can eat algae (if they are immune from it, which people are not anymore). the cleanest water has algae in it. algae, tree roots, fish, dirt, insects, and plants are natures water filter. filtering out the substances you do not need. the leftover substances that people call "unhealthy" are the things you should be immune to, preventing sickness from the bacteria in that particular ecosystem.