Since Shuswap and Mara Lakes are the source of drinking water for a large percentage of the region’s population, some residents have referred to the lakes as drinking water reservoirs due to their interest in maintaining high water quality. Yet, calling these lakes reservoirs is misinformed, as most lakes are complex ecosystems, that support a wide diversity of life forms and the biology of the lakes varies according to the season of the year and the variety of natural and man-made inputs. By and large, most of the Shuswap and Mara Lakes area is classified as oligotrophic with clear, relatively nutrient free water, as are most lakes in the Shuswap.
Lakes that contain higher levels of nutrients and thus higher concentrations of algae are called mesotrophic. Salmon Arm and Tappen Bays are mesotrophic, due to the slower flushing rate of the water in the bays and to the nutrients entering the lake from the sewage treatment plant, storm water and the Salmon River. Monitoring efforts are also showing an increase of nutrients in the Shuswap River, likely due to agricultural run-off. Gardom Lake is also classified as mesotrophic, due to the naturally occurring levels of nutrients and algae.