Water Quality photo identifier

Water Quality Program

Zostera japonica Management on Commercial Clam Beds in Willapa Bay General Permit

The Zostera japonica Management on Commercial Clam Beds in Willapa Bay permit is a combined National Pollutant Discharge Elimination System (NPDES) and State Waste Discharge General Permit. It allows the use of imazamox and marker dyes on commercial clam beds (excluding geoduck), in Willapa Bay only, for control of Zostera japonica eelgrass, a Class C noxious weed.

Proposed permit modification

Based on new scientific research and data, we are updating an existing, active water quality permit that allows commercial shellfish growers to continue to use the herbicide imazamox to control non-native eel grass in Willapa Bay. The growers requested the permit from Ecology several years ago because the non-native eel grass, Zostera japonica, is a noxious weed that makes it difficult to grow and harvest clams.

More information

When we issued the permit in 2014, we required the growers to study and verify that a 10-meter unsprayed buffer around the treatment area adequately protects native eelgrass and water quality. The scientific research and results came back showing that the application method is working as intended and confines the herbicide impact to the applied area. We have updated the permit based on the new data. Scientists from the National Oceanic and Atmospheric Administration, and state departments of Fish & Wildlife and Natural Resources reviewed the study data and did not recommend changes to the buffer. According to the U.S. Environmental Protection Agency, imazamox is practically non-toxic for mammals, fish, birds and invertebrates. EPA does not believe it poses a hazard to public health in or on food products. This permit is specifically tailored for commercial clam beds, and we reiterate, it’s for use in Willapa Bay only.


Submitting written comments

The public comment period ended 5:00 pm, March 7, 2017. We are reviewing comments received.

Workshop and Public Hearing

We held workshops and public hearings on these dates and locations:

Webinar and in-person
January 24, 2017 - 1:00 pm
Washington State Department of Ecology
300 Desmond Drive
Lacey, WA 98503-1274
In-person only
January 26, 2017 - 10:00 am
Willapa Harbor Community Center
916 W First Street
South Bend, WA 98586

Current Permit Documents

Annual Operations Reports

Historical Permit Development Information

Picture of a Willapa Bay Zostera japonica eelgrass bed from Dr. Kim Patten
Zostera japonica bed photo by Dr. Kim Patten

State NWCB Zostera japonica noxious weed listing

Aquatic Pesticide NPDES Permit ListServ