Revises provisions relating to the use of credible data to establish aquatic herbicide application permit conditions for irrigation drains or wasteways.

Declares that credible water quality data, for the purpose of chapter 90.48 RCW, includes surveys and studies done for the purpose of documenting threatened or endangered anadromous fish life stages and the suitability of irrigation district drains or wasteways to support complete fish life cycles, when those surveys or studies are used to condition permits issued under the provisions of the federal clean water act or this act.