This document updates the water quality objectives for Osoyoos Lake in order to help protect aquatic life, drinking water and recreation, now and into the future. These water quality objectives are proposed on the basis of an assessment of Osoyoos Lake water quality data collected over the past 40 years, and an evaluation of land use changes in the watershed. Nutrients, particularly phosphorus, have decreased in all three basins of the lake, and dissolved oxygen concentrations in the bottom waters of the north basin have increased in the fall. These changes are primarily attributed to decreases in point source nutrient loading to the Okanagan River upstream of Osoyoos Lake. A quantitative assessment of the non-point source nutrient load is not possible with the available data, however decreases in phosphorus load to Osoyoos Lake from septic tanks and other land uses are also likely. Over a multi-decadal time frame, Osoyoos Lake water quality has improved in trophic status from eutrophic to mesotrophic. Importantly, bottom waters of the north basin contain more dissolved oxygen in the fall now than in years past. The Okanagan River discharge, however, strongly affects nutrient concentrations in Osoyoos Lake on a seasonal and interannual basis, and significant internal phosphorus loading continues, particularly in the central and southern basins. As a result, water clarity has shown no change over time. The water quality objectives recommended here, take into account these background conditions and changes in land use. Continued population growth and development within the watershed, in addition to increasing recreational use, will present challenges to water quality protection in the future.
Jensen, Vic; Sokal, Michael; St Hiaire, Dan; Rieberger,Kevin; McQueen Don. 2012. Water Quality Assessment and Objectives for Osoyoos Lake: A First Update. Ministry of Environment. Working Paper
Topic: Water Quality
Keywords: Osoyoos Lake, water quality, Okanagan River, upstream
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