I grew up near Portage Lakes in NE Ohio. For much of my childhood, the water was a little murky, the seaweed wasn't too thick, and the lakes were pretty harmle

I grew up near Portage Lakes in NE Ohio. For much of my childhood, the water was a little murky, the seaweed wasn't too thick, and the lakes were pretty harmless (and fun) to swim in. Sometime around 2001, zebra mussels were accidentally introduced (the common theory I've read is by attaching to a boat that had been docked in Lake Erie prior to being brought back to Portage Lakes). The zebra mussels spread very fast and the lake noticeably changed. The water became much clearer. As a result, more sunlight could penetrate the water, and it could penetrate deeper, so much more seaweed grew. Personally, I hated them because they made swimming at our local park more dangerous. Their shells are sharp and will cut human feet pretty easily. That being said, in hindsight they did appear to clean up the water a lot. I wonder if they actually made the lake healthier for humans to swim in and live near as a result?