An implementation plan is a document, guided by an approved TMDL, that provides details of the actions needed to achieve load reductions, outlines a schedule of those actions, and specifies monitoring needed to document action and progress toward meeting water quality standards.

An implementation plan provides a framework for local stakeholders to use to reach the goals established in the TMDL.

An implementation plan generally includes the following elements:

• A list of actions needed to reduce pollutant concentrations
• A timeline for implementing the plan
• Reasonable assurances that implementation will occur
• A list of who will be responsible for undertaking planned actions
• An explanation of how progress on actions will be tracked
• A monitoring or modeling plan with milestones for measuring progress
• A description of how data will be evaluated and used to recommend revisions to the TMDL
• A schedule of dates by which water quality standards are expected to be met, including interim goals or milestones as deemed appropriate

Plans are developed by a variety of stakeholders including government agencies, local citizens, and the watershed advisory group (WAG) for the area. Designated government agencies and the WAG are generally the driving force behind the plan and are responsible for identifying appropriate implementation measures. DEQ serves as the repository for implementation plans and often coordinates, or assists in, developing the plan, writing the document, and prioritizing projects for implementation. However, it is often other agencies (such as the Idaho Department of Lands or the Soil Conservation Commission) that actually write the plan.

Idaho Code states that "designated agencies" are responsible for implementing the plan. Designated agencies are defined in Idaho Code as:

• Idaho Department of Lands (timber harvest, oil and gas exploration and development, and mining issues)
• Soil Conservation Commission (grazing and agriculture issues)
• Idaho Department of Transportation (public road issues)
• Idaho Department of Agriculture (aquaculture issues)
• DEQ (all other issues)

The U.S. Forest Service and the Bureau of Land Management, through governmental memoranda of understanding, also serve as designated agencies on the federal lands they manage.

Once an implementation plan is written and has been reviewed by the WAG, the designated agencies and others begin to implement the actions outlined in the plan. However, pollution control measures are often well underway before the plan is completed. Some pollutant control measures are in place before the TMDL is written and others are implemented during the TMDL/implementation plan writing process. Controlling pollutants is a long, on-going process, not something that occurs at just one point in time or just because an implementation plan has been written.

The term, "best management practice," or "BMP," is often used to describe the actions or methods taken to help achieve TMDL goals. A BMP is a conservation practice that has been found to be an effective means of preventing or reducing pollution from nonpoint pollutant sources. An example of a BMP for a grazed area with sediment or bacteria issues would be to construct a fence and use watering troughs to keep cattle away from the stream.