TMDLs may also be established for a portion or segment of a watershed. A TMDL, in actuality, is a planning document. Once this capacity is determined, sources of the pollutants are considered. Both point and nonpoint sources must be included. A technical definition exists in federal regulation at 40 CFR 122.2.
Examples are sheet flow from pastures and runoff from forest logging.
Current estimates indicate that nonpoint sources are the cause of 93 percent of the state's surface water quality problems. The MOS may not be the same for different waterbodies due to differences in the availability and strength of data used in the calculations. The allocations are simply the amounts of pollutants that can be discharged from each category. The TMDL does not specify how the dischargers must attain their particular load allocation. In other words, the TMDL will not set best management practices for a discharger or otherwise tell the discharger how to meet their goal, it merely sets their goal.