My ocean, stream, and pond has green edges...... How do I solve this?

My ocean, stream, and pond has green edges...... How do I solve this?

I’m guessing it’s from the poison frogs. At first it was only the pond, then I killed all the poison frogs but I left 2 so I could train a healer. I kept it that way for a couple of days and the green in the pond didn't spread, everything under control. Until I get sick the other day and paused the village time. Unfortunately, pausing it didnt have any effect, and when I got back everyone is sick except for 2. With 15 deaths... And the green spread to the ocean... Now it’s in the stream too....