Maryland to ban felt-soled waders, Alaska also ROCK SNOT: Algae can hitch a ride on the fibers, infect trout streams.

MONKTON, Md. -- As an algae with a gross nickname invades pristine trout streams across the U.S., Maryland is about to become the first state to ban a type of footgear the organism uses to hitchhike from stream to stream: felt-soled fishing boots.

The state Department of Natural Resources plans to prohibit wading with felt soles starting March 21 to curb the spread of invasive organisms that can get trapped in the damp fibers and carried from one body of water to another.

Similar bans will take effect April 1 in Vermont and next year in Alaska, aimed especially at didymo, an algae that coats riverbeds with thick mats of yellow-brown vegetation commonly called "rock snot."

Maryland fishery regulators say didymo, short for Didymosphenia geminata, can smother aquatic insect larvae such as mayflies, stoneflies and caddis flies that are favored food for trout and other fish.

"We've got to keep it from spreading," said Jonathan McKnight, associate director of the state Wildlife and Heritage Service in Maryland, where didymo was found in 2008 in the Gunpowder Falls north of Baltimore. A western Maryland stream, the Savage River, also has tested positive for the organism but hasn't had a rock snot bloom.

Didymo, pronounced DID-ee-moh, isn't a stream-killer like acid mine drainage. Fish have adapted in the northern rivers where it first appeared, but biologists can't say for sure how it will affect Maryland waterways.

"I think the cautionary approach to that would be to assume it's going to have some adverse impacts and respond accordingly," said Ron Klauda, a Maryland freshwater fisheries biologist.

Maryland officials are taking public comments through Feb. 28 on their proposed ban. They say 2011 will be an "education year," with violators getting warnings and information cards instead of tickets. Fines and penalties haven't been determined and won't be effective until 2012.

A U.S. Agriculture Department map shows didymo in at least 18 states as of 2008. New Zealand has banned felt soles to protect its trout fishery.

Some anglers and policymakers, however, aren't sold on the felt-sole ban. Many anglers prefer felt to rubber -- even newer, supposedly stickier rubber compounds -- because they believe felt gives better traction on slippery, rock-strewn riverbeds where losing one's footing can be disastrous.