If the pollution event is an emergency - putting people or natural resources at immediate risk - you should contact appropriate first responders.  In many parts of Tennessee, you should call 911. 
 
Most of the time, however, your first contact should be the environmental field office of the Tennessee Department of Environment and Conservation (TDEC). Call the local office and ask to speak to someone in water pollution control. You can request a site visit be conducted. TCWN always recommends documenting the pollution problem as much as possible - through photographs and by recording the data and time of problems.
 
You can also submit a citizen complaint - called a Section 118(a) complaint - following TDEC's procedures.  The Tennessee Water Quality Control Act provides for such complaints, and requires TDEC to respond to them.  These complaints can be fairly informal, but the more information you provide, the more likely it is that TDEC can do something about the problem.  For an example of a 118(a) complaint, click here.  You can also contact EPA Region 4 in Atlanta, though TDEC has the first line of enforcement authority.
 
If you observe a sanitary sewer overflow - raw sewage released from manholes or in a building - you should contact your sewage treatment plant first.  They can send out a crew to stop the leak and clean up the sewage.
 
If the problem is related to stormwater violations, you should also contact your city or county stormwater department.
 
And, of course, if you are not able to get the help you need from these public authorities, contact TCWN at 865-522-7007.