Does Anyone Know Why This Water is Green?

I was walking along a small stream in the forest when I noticed something strange. The water comes out of a large concrete pipe, and where it first collects, it's very green. I do not know why. It could be algae, or something completely different. The stream looks much clearer further downstream, but I still found myself wondering whether the water is actually healthy — especially for the animals living around it. So if anyone knows what might cause water to look like this, I'd genuinely love to hear your thoughts. I also found some signs of wild boar (again) further along the walk and picked up some rubbish that had been left behind. Maybe I'll eventually take a water sample and find out what's actually going on. For now, I'm just curious. There is Already Plenty to see when you let nature guide your way.