skip to content
Government of Western Australia - Department of Fisheries
Wednesday 14 December 2022

Blue swimmer catches in the Swan and Canning rivers - clean your crabs carefully

Testing is being carried out every week in the Swan and Canning rivers for Alexandrium, an algae which can produce Paralytic Shellfish Toxins (PSTs). 

So far this season water sampling tests have been clear, but this specific toxic algae has been detected within the river system every summer since 2019 and fishers are urged to clean their crabs carefully.

PSTs accumulate in some seafoods including mussels and in the guts (mustard) of crabs. Eating affected crab mustards or mussels may be dangerous, causing severe illness and, in extreme cases, even death. If you feel unwell after consuming crab or mussels, seek prompt medical attention and save any remaining seafood for testing.

  Harmful algae caution signs have been installed along the rivers

It’s important that recreational fishers who catch blue swimmer crabs in the Swan and Canning rivers clean and prepare them correctly by removing the head, guts (mustard) and gills before freezing, cooking or eating the crab meat.

Cleaning crabs should happen at home because fishers are required to take blue swimmers home as whole crabs, unless they plan to cook and eat them on the river foreshore.

Cooking or freezing whole crabs does not destroy PSTs and cooking crabs with their heads, guts (mustard) and gills attached could potentially concentrate or spread the toxin from crab guts into the flesh or broth. 

Freezing crabs (with guts still in place) could also result in PSTs spreading to the flesh during thawing. Comprehensive instructions, on how to clean blue swimmer crabs properly, are available here in a brochure and this video to assist recreational fishers.​

For the current season, harmful algae caution signs have been installed at popular jetties, boat ramps, bridge crossings and fishing locations. They are part of a comprehensive and ongoing Alexandrium education campaign by the Department of Primary Industries and Regional Development (DPIRD) and the Department of Biodiversity, Conservation and Attractions (DBCA). See their FAQs​ for more about this toxic algae.

DBCA continues to monitor water quality in the Swan Canning estuary during the crabbing season and if the algae reach levels of concern, DPIRD will collect crabs for testing. 

The Department of Health also advises caution when eating shellfish – including mussels, oysters, clams, pipis, scallops, cockles and razor clams – from the Swan and Canning Rivers. Urban waterways can contain algal toxins, heavy metals, microbial and other contaminants that affect the quality of shellfish. The Department of Health recommends people only consume shellfish harvested commercially – under strict monitoring programs – to ensure that the waters are free from pollutants and toxins. 

Last modified: 14/12/2022 3:03 PM

© All contents copyright Government of Western Australia. All rights reserved. ABN: 18 951 343 745


© This work is copyright. You may display, print or reproduce this material only in an unaltered format for your personal or non-commercial use, or for use within your organisation. Apart from any use permitted under the Copyright Act 1968, all other rights are reserved.


The information and advice provided by the Department of Fisheries website is made in good faith and is from sources believed to be reliable and accurate at the time of release onto the website. Changes in circumstances after a document is placed on the website may affect the accuracy of the information. Full disclaimer details are available at