Didymo (Didymosphenia geminata) is a type of algae found in fresh water. Commonly known as “rock snot,” didymo can form thick, brown mats on stream bottoms. During blooms, didymo can cover long stretches of streambeds and can disrupt the organisms that live in and on the streambed. This can have an adverse affect on fish by limiting their food supply.

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Phosphorous and Didymo

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Didymo (Didymosphenia geminata) is a type of algae found in fresh water. Commonly known as “rock snot,” didymo can form thick, brown mats on stream bottoms. During blooms, didymo can cover long stretches of streambeds and can disrupt the organisms that live in and on the streambed. This can have an adverse affect on fish by limiting their food supply.

Didymo has been found in New York, Alberta, British Columbia, Idaho, Kentucky, Maryland, New Hampshire, South Dakota, Tennessee, Vermont, Virginia, and West Virginia. In New Zealand, didymo has been particularly pernicious. Under the New Zealand Biosecurity Act of 1993, the entire South Island is a Controlled Area. People are legally obliged to prevent the spread of unwanted organisms and can face a penalty of up to 5 years and/or a fine of up to $100,000 for knowingly spreading didymo.

The accepted methods of curtailing the spread of any nuisance species applies to didymo:

  • Check any gear and remove all obvious clumps of algae.
  • Clean all items using very hot water (above 60 degrees centigrade) for at least 20 minutes. As an alternative, soak items in a 2% solution of bleach and water or a 5% solution of salt and water. Absorbent items, such as felt-soled waders should be soaked for at least 45 minutes in hot water kept above 45 degrees centigrade.
  • Dry all equipment thoroughly before taking it to a new watershed.

New research, though, by P. V. Sundareshwar, et al, writing in the journal Geophysical Research Letters, indicates that didymo is able to concentrate phosphorus from the water. Didymo can, as a result, grow in streams that are considered relatively clean.

This provides additional incentives to keep phosphorus out of our waters.

One thing that we all can do, and it is very simple, is to make sure that any lawn fertilizer that we apply goes on the target area. If granules of fertilizer, of which phosphorus is a component, end up on your sidewalk, sweep them up and place them on the lawn. Fertilizer granules on hard surfaces run directly into the watershed where they could contribute to didymo blooms.

The mantra of check, clean, and dry is certainly sage advice. These steps should be followed to prevent the spread of any nuisance species. Keeping phosphorus out of the watershed by preventing runoff from the home can help as well.

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