Protecting Local Waterways Through TMDL Implementation

In March 2021, the City of St. Helens was formally notified by the Oregon Department of Environmental Quality (DEQ) that it had been designated as a Designated Management Agency (DMA) for the Willamette River Basin. This designation recognizes the City’s regulatory responsibility for managing and protecting water quality within its jurisdictional boundaries.

The Willamette River is a major waterway in Oregon, discharging an average of 22.73 million acre-feet of water annually into the Columbia River. One of the river’s most significant tributary systems is the Lower Willamette Subbasin, which includes the northernmost area where St. Helens is located. Within the City limits, Milton Creek and McNulty Creek are considered important tributaries to the Lower Willamette River Subbasin and play a direct role in the overall health of the watershed.

As a DMA, St. Helens has legal authority and responsibility over impaired surface waters that contribute pollutants within its jurisdiction. These impairments are identified in the Total Maximum Daily Load (TMDL) established under the Willamette Basin Water Quality Management Plan. In practice, this means the City must implement measures that reduce pollutant loading and improve water quality in its streams, creeks, and stormwater systems.

To meet these obligations, the City is required to:

• Develop and submit a TMDL Implementation Plan to DEQ in accordance with Oregon Administrative Rule (OAR) 340-042-0080;
• Outline strategies, best management practices (BMPs), and measurable actions to address pollutants of concern; and
• Provide annual reports to DEQ documenting progress, challenges, and outcomes of implementation activities.

Through this designation, the City of St. Helens plays an essential role in advancing the shared state and regional goal of protecting the Willamette Basin’s water quality for ecological health, recreational use, and community well-being

What is a TMDL?

TMDL stands for Total Maximum Daily Load. It is a water quality standard established by the Oregon Department of Environmental Quality (DEQ) that identifies the maximum amount of a pollutant a waterbody can receive and still meet water quality standards.

In St. Helens, we are responsible for addressing pollutants such as:

• Mercury – a toxic pollutant that can accumulate in fish and pose health risks to people and wildlife.
• Temperature – warmer water temperatures can harm salmon, steelhead, and other cold-water fish that rely on cool, clean streams

In addition to mercury, the City of St. Helens is also required to address temperature as part of its TMDL obligations. Warmer water temperatures can negatively affect salmon, steelhead, and other cold-water fish that depend on clean, cool streams.

The Temperature TMDL Implementation Plan is currently under development and will be submitted to the Oregon Department of Environmental Quality (DEQ) by November 9, 2026. Until that plan is finalized, this webpage will focus on the City’s Mercury TMDL Implementation Plan. Updates will be shared here as the Temperature TMDL plan progresses

Together, we can protect the waterways that make St. Helens a safe, healthy, and beautiful place to live.