Scientists have been worried about the herring population in Lake Superior recently. In fact, last year they warned it might collapse.
Lake Superior is the only one of the Great Lakes with a large population of this native fish.
This fall, new rules protecting herring took effect in Wisconsin and Minnesota and things appear more stable.
But there may still be a big problem lying beneath the surface.
Lake herring are also called cisco. They thrive in Lake Superior like few other places in the world.