Reddit an Fishing Wiki just launched a new comprehensive section with state by state numbers to report poachers.
Regulations exist to protect the fish, so please do not tolerate anyone you see poaching or even just bragging about poaching. Report it immediately by dialing 911 and saying you would like to report a poaching in progress. The police will connect you to the nearest wildlife officer if they are on duty, or otherwise deal with the poachers themselves. States will also usually have a designated poaching phone line, text service, and email service available. On top of keeping fishing opportunities available for everyone, you can be given a monetary reward for turning them in.
To see the state by state breakdown click here: Poachers State by State
To see a poacher get caught after an intense foot race, view below: