Stop the Spread of Invasive Species Like Didymo & Whirling Disease

One of the biggest threats to our fisheries is the spread of invasive aquatic species. Whirling disease, the New Zealand mud snail, and Didymo have all either impacted trout fisheries or pose a potential risk to their survival. Tennessee’s trout fisheries are not immune to these invaders, but their spread is preventable. It requires action on the part of fly fishers and other anglers.

Whirling disease is perhaps the best known of these threats. It is a parasite that infiltrates the head and spinal column of fingerling trout where it causes the fish to swim erratically and eventually die. The stocking of live infected fish is a primary method that the parasite is introduced to new rivers. However, it can also be spread by humans who carry the parasite unknowingly on their wading equipment after fishing in infected waters. The whirling disease spore can live dormant for as long as 30 years.

The New Zealand mud snail had spread at an alarming rate throughout the West and threatens other waters. These incredibly small snails have no natural predators in North America and their swift rate of reproduction overwhelms a river’s ecosystem. These snails don’t have a direct effect on trout, but have negative impacts on aquatic insects that are the foods trout feed on. Mud snails can easily attach to wading equipment. A single mud snail has the capability of cloning itself where it can destroy a stream’s complex food web.

New Zealand Mud Snails

New Zealand mud snails are exceptionally small and can completely cover the bottom of a river 

Didymosphenia geminata, better known as didymo, is present in many of our Tennessee trout rivers and could threaten other. It is a single cell algae that thrives in cold, clear waters. It attaches to rocks and aquatic plants and forms massive mats that resemble shag carpet. Didymo smothers areas where trout lay eggs. It also competes with native species that aquatic insects feed on. Loss of food for aquatic insects means a loss of food for trout. Again, this exotic species is spread by the wading equipment of fishermen.

Didymo is currently in the Clinch, South Holston, Watauga, and Holston Rivers. You may have heard it referred to as “rock snot” which is a pretty apt description. It is most obvious in the Clinch and South Holston, but no one is certain of what the exact effects will be. Fisheries biologists at Great Smoky Mountains National Park are also concerned that it could be spread to the streams of the Smokies.


You may have seen Didymo growing on rocks and vegetation on East Tennessee’s tailwaters 

As fishermen we have the potential to spread these creatures to new waters and potentially devastate our fisheries. However, simply cleaning your wading boots, gravel guards, and the feet of your waders can prevent the spread of these organisms. This is extremely important to prevent the spread of these invaders.

A study conducted by Montana State University sought the quantify how serious the threat is for anglers to spread these aquatic hitch hikers. Researchers approached anglers on the stream and 487 agreed to participate over the course of the study. Researchers simply rinsed the sediment from anglers’ boots and waders of anglers who agreed. Sediment that was rinsed from fishermen was scanned for exotic hitchhikers. The study found that the average angler carried 16.8 grams of sediment on their boots and waders. This study was conducted over several rivers in western Montana. To find the true effects of sediment transfer researchers checked fishing license sales in the same area and estimated that the number of anglers fishing over a 30 day period in the study area could have moved as much as 3 tons of sediment just with their wading boots!

It has already been proven that Didymo, whirling disease, and New Zealand mud snails can be transported via felt wading boots so it’s imperative that we all rinse our boots after fishing rivers like the Clinch, Holston, South Holston, and Watauga. This will prevent the spread of these organisms to other rivers, perhaps your home water.

You can click on the following links to learn more:


Whirling Disease

New Zealand Mud Snail

Hazel Creek Campout Autumn ‘08

Turneffe Flats Belize