Don't Spread Didymo


Help Us Keep Didymo Out of Missouri

Rock snot. Sounds a lot worse than “Didymosphenia geminate,” doesn’t it? This invasive alga is also commonly known as “didymo,” but no matter what you call it, it's gaining footholds in streams worldwide, including some of the most revered trout waters on Earth. The infestation nearest to Missouri is in the White River just south of the Missouri-Arkansas border.

Didymo is Bad News for Anglers

The jury is still out concerning didymo’s possible ecological effects. But rock snot is definitely bad news for anglers. Stringy alga threads catch on all types of hooks, from dry flies to crankbaits, making fishing nearly impossible.

When Fishing: Comply with the Porous-Soled Wader Ban and Wash Your Waders

Contamination of recreational equipment, such as boats, life jackets and fishing gear, particularly waders, is the most common way for didymo to spread.

  • Don't wear porous-soled waders when fishing in trout parks, trout streams, Lake Taneycomo and buffer areas. Learn more about the porous-soled wader ban.
  • Treat your porous-soled waders to avoid spreading didymo in Missouri.

At Home: Check and Clean Your Gear

  • Check all gear and equipment after use and remove any visible algae.
  • If you notice algae on your equipment at a later time, do not dispose of the algae by putting it down a drain. Dispose of it in the trash.
  • Clean all equipment with a 2 percent household bleach solution, 5 percent saltwater solution, or dishwashing detergent. Allow all equipment to stay in contact with the solution for at least 3 minutes.
  • Soak all soft items, such as felt-soled waders and life jackets, in the solution for at least 20 minutes.
  • Dry all equipment in sunlight for at least 48 hours.
  • Consider replacing felt-soled waders with a new, environmentally sensitive alternative.


A closeup of a clump of didymo that has been picked up from the water in someone's hand
Didymo looks slimy but feels coarse.
MAF Biosecurity NZ
Photo of man holding a wad of didymo
Didymo is an invasive algae that forms slimy mats that smother fish eggs and makes water sports unpleasant.  New Zealand Fish and Game

Treating Felt-Soled Waders

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