Zostera japonica management on commercial clam beds in Willapa Bay general permit

We issue coverage under this general permit when shellfish growers choose to use an aquatic herbicide (imazamox) to control the non-native eelgrass Zostera japonica on their commercial clam beds. This permit does not cover herbicide use on geoduck or oyster beds, or regulate physical or mechanical control methods. Zostera japonica is listed as a class C noxious weed because it can cause significant impacts on clam aquaculture and harvest for the shellfish industry in Willapa Bay. Read our blog to find out more about the Zostera japonica permit.

The current permit expired on March 3, 2025. The new permit is effective on May 2, 2025 and expires on May 1, 2030. Although the current permit has expired, it is still in effect until the new permit becomes effective. 

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Permit documents

We are pleased to announce that we are reissuing the Zostera japonica Management on Commercial Clam Beds in Willapa Bay General Permit. A formal announcement was published in the Washington State Register on April 2.

Effective May 2, 2025

Public process

We invited public comments on the draft general permit documents beginning Nov. 21, 2024 through Jan. 14, 2025. We also held two workshops and public hearings, both online and in-person. During the workshops in December and January, we explained the proposed changes to the permit and answered questions before the public hearings began. Appendix C of the final fact sheet, linked above, shows our response to those comments.

Click the map to enlarge.

Documents from the draft 2025 public comment period

Map of treatment areas

This map shows where treatments to control Z. japonica have been done between 2019 - 2023. An average of 82 acres of clam beds were treated each year during this time. The total area of Willapa Bay is around 80,000 acres, with approximately 8,000 acres covered by the native eelgrass Z. marina, and about 6,000 acres covered by the invasive eelgrass Z. japonica

Permit application, forms, and resources