It was 3 inches long it has 6 legs and its body looks like it is segmented. And it looks like it has feelers. I was near the Mississpi River in Minnesota and walking along the rocks above my head.
Your photo is of a giant stonefly nymph.
These nymphs feed on plant material and algae. The adults do not feed, but can be attracted to lights at night.
Weeks before they hatch, stone fly nymphs will start to migrate to the banks of the river where they live. So that is why it was on a rock above your head.
These larva are favorite food of trout as well as other fish and some birds. They are a good indicator the stream/river is clean as they need plenty of oxygen to breathe.
The family of giant stoneflies are often called salmonflies – that is a common name, which can cause confusion, depending on where you live different species have different common names. That is why it is important to use scientific names, however, I do not always list the scientific name since it is not commonly used. The genus Pteronarcys is for the group of Giant Stoneflies. Giant stonefly is the accepted common name as all insects in the Order Plecoptera are known by entomologists as stoneflies. As I noted originally, stoneflies are an important food of trout and other fish. This does include salmon (hence the common name) and are a favorite bait of anglers. If you Google the name giant stonefly, you will only get info on the genus Pteronarcys.
(Note – I write the word stonefly using one word not two. If you separate the fly from the word then an entomologist knows it is a true fly in the Order Diptera – two wings only. When attached to the first word like stonefly, dragonfly, dobsonfly, or scorpionfly, we know it is in a different order and has 4 wings.)