City of Lake Oswego 2025 Water Quality Report Your 2025 Water Quality Report is based on data collected during the 2024 calendar year. The City of Lake Oswego prepares this report in accordance with Federal and State regulations to bring our customers the best available information about the water they drink.
Where does Lake Oswego’s water come from? Your drinking water originates in the Clackamas River watershed, which is one of the highest quality water sources in the state. This watershed encompasses 940 square miles and begins in the Mount Hood National Forest. Water is withdrawn from the Clackamas River, then pumped through a pipeline buried beneath the Willamette River to the Lake Oswego Tigard Water Treatment Plant located in West Linn. A Clackamas River Watershed Source Water Assessment was completed in 2019. The report is available at www.deq. state.or.us/wq/dwp/docs/uswareports/USWA_00457LakeOswego.pdf. An additional Clackamas River Water Providers report can be found at https://storymaps.arcgis.com/collections/d107e2dad24e4a5d9c28dad37a835c16
Sources of Contaminants In order to ensure that tap water is safe to drink, the EPA sets regulatory limits on the amount of certain contaminants in water provided by public water systems. The U.S. Food and Drug Administration sets limits for contaminants in bottled water which must provide the same protection for public health. The sources of drinking water (both tap water and bottled water) include rivers, lakes, streams, ponds, reservoirs, springs and wells. As water travels over the earth’s surface or through the ground it dissolves naturally occurring minerals and, in some cases, radioactive material. Drinking water can pick up substances resulting from the presence of animals or from human activity. Contaminants that may be present in source water throughout the United States include: o Microbial contaminants, such as viruses and bacteria, which may come from wildlife or septic systems e.g. coliform and giardia. o Inorganic contaminants, such as salts and metals, which can occur naturally or result from urban stormwater runoff, industrial or domestic wastewater discharges or farming. o Pesticides and herbicides, which may come from a variety of sources such as farming, urban stormwater runoff and home or business use. o Organic chemical contaminants, including synthetic and volatile organic chemicals, which are byproducts of industrial processes and may come from gas stations, urban stormwater runoff, and septic systems. o Radioactive contaminants, which can occur naturally, e.g. radon.
Cyanotoxin Monitoring Rule In 2018, the Oregon Health Authority (OHA) developed a drinking water rule that requires many drinking water systems in the state to test for cyanotoxins, and notify the public about the test results. Cyanobacteria naturally occur in lakes and streams. Under certain conditions, such as in warm water containing an abundance of nutrients, they can rapidly form harmful algal blooms (HABs). These blooms are capable of producing toxins known as cyanotoxins. Cyanotoxins are compounds that are capable of harming humans. The OHA has issued safe drinking water limits for the cyanotoxins microcystins and cylindrospermopsin. Lake Oswego’s results are listed below. Algal Toxin
Health Advisory (Vulnerable Population)
Health Advisory (All Population)
Health Advisory (Recreational Advisory)
Sample Date
Raw Water
Total Microcystins
0.3 µg/L
1.6 µg/L
4 µg/L
2024
Not Detected
Cylindrospermopsin
0.7 µg/L
3 µg/L
8 µg/L
2024
Not Detected