Didymo
Threat to Trout Fisheries
“Didymo” (Didymosphenia geminata) is a diatom, a
form of algae, which is native to the northern hemisphere. Up
until recent years, it occurred at low levels in pristine lakes
and streams but has become invasive, forming dense mats in many
streams in North America. In close proximity to Oklahoma, Didymo
has been found in Colorado and the White River in Arkansas. This
invasive species attaches to rocks and plants in streambeds and
may impact freshwater fish, aquatic plants, and important
aquatic insects. Didymo can completely smother rocks and plants
and reduce the area of clean substrate on which fish need to
spawn and feed. It also tends to outcompete native algal
species, many of which are food for aquatic insects, the main
diet source of native stream fishes. Didymo mats has become so
thick in some areas it became impossible to fish those stream
stretches.
Didymo is particularly fond of cold tailwaters and, as such,
poses a particular threat to the trout fisheries in the Lower
Illinois and Lower Mountain Fork Rivers. Anglers have been
principle means of spread, making trout anglers who fish streams
in the western United States and Arkansas and return to fish the
Lower Illinois and/or the Lower Mountain Fork in particular need
of taking precautions to avoid spreading Didymo to state waters.
Anglers need to take the following precautions to avoid
spreading Didymo:
- Before leaving the river, remove all plants and algae from shoes, waders, life vests, boat hulls, trailers
-
Treat equipment with a 2% bleach solution or a 5% salt solution or dishwashing detergent
-or-
-
Dry equipment for 5 days before fishing a different stream
-
Never transfer fish or plants from one body of water to another
-
Avoid using felt soled waders
-
Avoid wading through mats of Didymo
