Sargassum muticum

Identifying Features

  • Pale yellow to dark brown seaweed.
  • Grows near the surface.
  • Can be over a metre in length.
  • When held up out of the water, the side branches hang like clothes on a washing line.
  • Found mainland Scotland and Norway.


  • Entangles boat propellers.
  • Fouls harbour, marina and aquaculture structures.
  • Dense mats of detached weed hinder marine recreation and rot on beaches.
  • Replaces native seaweeds.

Wireweed in the sea. Image: P Brazier (CCW) © Crown Copyright 2009

Wireweed out of the water, the side branches hanging down in their characteristic fashion. Image: GB NNSS © Crown Copyright 2009