Photograph 1a. Riffles support many types of benthic algae in the upper Clackamas River upstream of Carter Bridge. (Photograph by Kurt Carpenter, U.S. Geological Survey, June 2010.)

Photograph 1b. Prasiola sp. (green algae) on the large cobbles in the Clackamas River downstream of River Mill Dam near Estacada. (Photograph by Kurt Carpenter, U.S. Geological Survey, April 23, 2006.)

Photograph 1c.Prasiola sp. (green algae) on a cobble from the Clackamas River downstream of River Mill Dam near Estacada. (Photograph by Kurt Carpenter, U.S. Geological Survey, June 2010.)

Photograph 1d. Stalked diatoms (Cymbella sp.) on a cobble from the Clackamas River downstream of River Mill Dam near Estacada. (Photograph by Kurt Carpenter, U.S. Geological Survey, June 2010.)

Photograph 1e. Nostoc sp. (blue-green algae) colony balls on a cobble from the upper Clackamas River upstream of Carter Bridge. (Photograph by Kurt Carpenter, U.S. Geological Survey, June 2010.)

First posted February 11, 2013