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Didymo infestation covering a whole riverbed.
Didymo covering rocks in a riverbed.

Didymosphenia geminata (didymo), also known as rock snot is a freshwater diatom (a type of alga). Didymo is currently found in a number of South Island rivers.

The Ministry for Primary Industries has declared the entire South Island a Controlled Area for Didymo. This means waterways are open to recreational activities, but people are legally obliged to prevent the spreading of didymo.

Check, clean, dry

CHECK: Before you leave a river or lake, check items and leave debris at site.

CLEAN: There are several ways to kill didymo.

DRY: Drying will kill didymo, but slightly moist didymo can survive for months.

Further Information

Go to the MPI website for more information on didymo