Rocky Mountain Ridged Mussels (Gonidea angulata) are listed under the Species at Risk Act (SARA) as a species of special concern and have been re-assessed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) as endangered. These fresh water mussels are only found in Canada in the Okanagan Valley of British Columbia. As a continuation of previous work and to inform future assessments and conservation efforts within this geographic range, seven easily accessible sites known to have high densities of G. angulata were selected as prospective index sites to monitor relative abundance (i.e. mussel bed density) using snorkel surveys. For lake sites, a two-stage sampling design was conducted using transects and quadrats. For the river site, cumulative counts from sides of the river were collected. Some sites were sampled only once while others were sampled multiple times from 2011-2016. Mean mussel densities across all surveys ranged from 0.19 to 2.86 mussels/m2, corresponding to site abundance estimates ranging from 102 to 3,276 mussels. Depth measurements were also taken at most sites to inform the Fish Water Management Tool of the Okanagan Water Management Board.