No it doesn't, it breaks down. The mere action of current and water action
rubbing it against the snag or the rocks and once free as it tumbles along
means it breaks down into minute pieces pretty quickly unless it is in
virtually stagnant water and I can't imagine that would happen often. While
it may not biodegrade, it does break up into pieces so small it offers no
real environmental problem.

--
Clark Reid
http://www.dryflynz.com
Umpqua Designer Flytier