I put 20 in my 1-acre pond and had them for a dozen years until a winter fish kill. They grew to 20 to 24 inches and I never saw any offspring�s. My bass did a complete job of eating them. I had every one of them named like pets. I'm sure they stir up the water some but in my case how can you tell. Most ponds get healthy pea green bloom and visibility drop to a foot or two. With my 20 KOI and 6 Israeli carp I never had any algae problems.