A TMDL is the maximum amount of a pollutant a body of water can assimilate without violating water quality standards.  A "maximum load," which is a mass/time unit, is usually derived from a  "concentration target."  There is an example of this process in the Knife River TMDL section. Click Here for a brochure we put together explaining TMDLs (based on Miller Creek).

How do we chose which stream or lake gets a TMDL?

The State of Minnesota, through the Clean Water Act, is required to update a list of impaired waters every even year.  Impaired waters are those that are not meeting their designated uses due to not meeting the water quality standard for those designated uses.

What are Impaired Waters?

Streams are organized by "Use Classes" (designated uses), such as swimming, navigation or habitat. Each class may have different standards for many different types of pollutants. For example, if "recreation" is a designated use for a river or lake, fecal coliform bacteria levels need to be very low in order to insure that swimmers and boaters do not get sick from being in the water. If high numbers of fecal coliform bacteria are found in a water sample, one may conclude that there has been recent fecal contamination, although not necessarily human in origin. When a waterway is designated as "impaired," it does not meet the standards designated for its use class.  Minnesota's impaired water list is called the 303(d) list. Once a water is listed, the state must develop a TMDL within 15 years of being listed. Read the MPCA fact Sheet on TMDLs here.

The Minnesota Pollution Control Agency (MPCA) administers the program at the state level, while the Environmental Protection Agency "approves" all TMDLs at the federal level. The MPCA can contract out the work of developing a TMDL. The SWCD has been contracted to develop both the Knife River TMDL (Turbidity)  and the  Miller Creek (Temperature Impairment).TMDLs.