Abstract
A survey was conducted in August 2008 to determine the distribution and extent of stalked diatoms in major rivers and streams in Grand Teton National Park (GTNP). We determined that a nuisance bloom of the diatom Didymosphenia geminata was present in Lake Creek from the outlet of Phelps Lake to approximately 1 km downstream of the Rockefeller Preserve. This bloom was considered "excessive" because the coverage of the stream substrate was 70% or above for greater than 1 km. This diatom species is able to survive out of water in damp conditions, and it may be transported on the gear of recreationalists. In GTNP, this diatom was found in a high visitor use area, with concomitant potential for the species to be spread by anglers to other sites within the national park. Although there are several factors that appear to influence its distribution, recent nuisance blooms of this species suggest popular angling sites are often sites of nuisance blooms. Decontamination of aquatic gear by recreationalists may be appropriate to limit the spread of nuisance blooms within the national park system and adjacent public and private water bodies