Did you get to swim in a lake over the summer? Was the water clear, cool, and fresh? Or was there slimy green algae? Maybe algae levels were so high that the lake was closed.

A big spike

Recently scientists tested 80 lakes across Canada. They found that algae has been increasing in most of them since the mid-1800s. 

From 1850 until 1966, algae levels slowly increased. Then, they suddenly shot up. Today, algae levels are seven times higher than they were in 1966. That’s a lot of algae growth!