Water Environment (Water Framework Directive) Regulations River Basin Management Plan Cycle 3 intertidal opportunistic macroalgae classification data used for the UK Marine Strategy Article 8 biodiversity assessments for the UK Regional Seas. The WER opportunistic macroalgae method statement and classification tool ('Opportunistic Macroalgae_ CoC_tool _CAPTAIN_v12.8_UKTAG.xlsm’) used to calculate WER Ecological Quality Ratios are available at https://www.wfduk.org/resources%20/transitional-and-coastal-waters-opportunistic-macroalgae. Project coordinated by the Environment Agency and Joint Nature Conservation Committee. River Basin Management Plan Cycle 3 opportunistic macroalgae data held by the relevant WER Agency.