You'll often hear the term "TMDL" in water-pollution discussions, because many of the actions we take to reduce pollution are based on this scientific measurement.

TMDL stands for Total Maximum Daily Load, which is the maximum daily amount of a pollutant that a body of water can absorb without violating water quality standards. A non-scientific definition for TMDL could be "pollution limit."

Pollutants in Delaware waters are often chemicals, such as nitrogen and phosphorus from fertilizer runoff, but TMDLs could also be set for such other pollutants as bacteria, sediments, or even heat --- anything that can injure a waterway's natural health.

Pollutants can come from specific "point" sources, such as sewage treatment plants, or from "nonpoint" sources, such as runoff from lawns, farms, parking lots and golf courses.

TMDLs have so far been established for the watersheds that drain into the Inland Bays, the Nanticoke River, the Appoquinimink River, the Christina River, Broad Creek, Red Clay Creek and White Clay Creek. As more than 90 percent of Delaware's waterways are considered "impaired," TMDLs will have to be set for many more waterways over the next few years. The deadline for setting them is 2007.

Setting pollution limits is just the first step toward improving water quality --- the important next step is the development of "pollution control strategies," which is the mission of the Tributary Action Teams.