I had a good sized pond( about 1/4 acre) in my former house up north..We'd get an algae bloom every spring. The lawn people put in a chemical..it took care of it for 20 years. We had tons of frogs, lots of small fish, a few snapping turtles..never bothered them.In 2001, the EPA banned the stuff. We tried others, but no luck...the algae was disgusting. Someone suggested we try koi..so next sping I spent about $1000 for three dozen decent sized koi. It was fun to watch them. Three days later, I see two grey herons in the pond, scarfing up the fish..then a week later, a pair of otters had dropped in..Great to watch..we had all the neighbors coming by..they stayed for about two weeks..ate all the fish..then left..
The algae stayed..