There are ways to see how the color changes in response to light/dark or in response to just letting the water set still and see if the green settles out.

but if it is suspended green in the water then it probably is a 'bloom' of algae or small 'plankton'.

It is very hard to have a nice clear swimming pond and a fertile pond for growing and supporting all species of fish at the same time. Swimming ponds need to be almost sterile of nutrients and suspended critters to stay clear. On the opposite end of the spectrum, most folks who manage their pond for healthy and growing fish want the whole food chain to be very strong. Thus they would see a bloom to be a huge plus as it means that the micro-organisms have tons to eat.

of course heavy blooms that don't go away can mean too many nutrients and can consume too much oxygen leading to oxygen crash and dead fish. That is nature's way of removing the excess biomass and to try to restore balance again.

A 1-2 week bloom should be no problem. Certain blooms are not good on humans so other experts may weight in here and say that your kids shouldn't swim.

Google pondboss and 'jar test' for more info on this.

algae blooms do not necessarily mean that there is too much nutrients.

there are a lot of strategies to reduce nutrients, plants can be helpful, stocking tilapia and having them die at the end of the season can help, consider adding a dark pond dye to reduce sunlight penetration which can also help with the aesthetics of the look of the pond which seems to be your main concern.

edit...just checked and allow it appears that you can commercially raise tilapia in IL you cannot stock them in your pond is that true?

others can weigh in soon as well...

Last edited by canyoncreek; 06/14/18 10:55 AM.