Didymo Algae
A particularly bad Didymo outbreak.

The Missouri Department of Conservation announced that it has instituted a ban on porous-soled boots and waders made of porous materials on waterways throughout the state. This announcement adds Missouri to the slowly, but steadily growing list of states that have made the decision to ban felt soled boots and other problem materials in the hopes of preventing the spread of invasive species, particularly Didymo algae.

Didymo (Didymosphenia geminata), commonly known as "rock snot", is an invasive algae that thrives in some cold water habitats, forming thick mats on river and stream bottoms. The algae reduces the amount of food available to other aquatic species and, in particularly bad outbreaks, can make fishing completely impossible.

Any fishing gear that harbors moisture for any extended period of time presents an opportunity for didymo to spread. Algae cells become trapped in moisture-holding materials, such as the felt common on the soles of traditional fly fishing gear. As this gear travels between water bodies, algae from one location can be transported to another.

Due to the extreme environmental and economic consequences of didymo invasions, some states are banning problem materials. Previous to Missouri's ban, Alaska, Vermont and Maryland have placed similar bans. Montana and Oregon are currently weighing legislation that would put similar bans in place.