2011 Aquatic Weed Surveys in Timothy Lake, Lake Harriet and North Fork Reservoir : final report

Abstract

Portland General Electric (PGE) was issued a new license by the Federal Energy Regulatory Commission (FERC) for the continued operation and maintenance of the Clackamas River Hydroelectric Project No. 2195 (Project) on December 21, 2010. This Project is located on both the lower 16 miles of Oak Grove Fork of the Clackamas River (Oak Grove Fork) and the mainstem of the Clackamas River in Clackamas County, Oregon. The effects of relicensing this Project were addressed in the Final Environmental Impact Statement (FEIS) completed in December 2006 and included the issue of invasive aquatic weed species. The term “aquatic weed” is used here to refer to any non-native aquatic plant species. Surveys of Timothy Lake conducted by Portland State University (PSU) in 1996 and a subsequent survey of Timothy Lake and Lake Harriet in 2004 did not locate any problematic aquatic weed species. However, repeated monitoring is necessary to detect infestations in a timely fashion and, if noxious weeds are present, to allow treatment when weed cover is low and eradication efforts more cost effective. With that aim, PSU conducted aquatic vegetation surveys of Lake Harriet, Timothy Lake, and North Fork Reservoir between August 31 and September 13, 2011. The purpose of these surveys was to detect any populations of aquatic weeds occurring in the lakes while also establishing baseline information reading native aquatic vegetation abundance and distributions in each waterbody.