Current Conditions

as of March 19, 2024 1:33am
0.0 in | 50.1° F | 54.4° F | WSW 0.2 MPH gust to 0.2 MPH | 98.63' above sea level

Water Quality

The Lake Oswego Corporation (LOC) has a longstanding water quality program with a goal of reducing harmful cyanobacteria blooms and stopping the introduction of invasive species. We accomplish this by having a robust program of testing and monitoring to guide our efforts. We began weekly testing and data collection in the early 1990s and have had a full-time limnologist on staff since 1999. To reduce the threat of zebra mussel, quagga mussel, and milfoil introductions, in 2000 the LOC initiated a (novel at the time) boat tagging and decontamination program which continues to this day.

Sampling data led the LOC to initiate several water quality improvement projects over the years with the goal of reducing phosphorus to a point where cyanobacteria are not the dominant phytoplankton population. These projects included reducing flow from the Tualatin River, installing hypolimnetic aeration, formulating phosphorus-free fertilizer for lakeside residents, dredging high-nutrient sediment, reducing leaks through our hydroelectric plant, and treating incoming water and the lake with aluminum sulfate. All of which have greatly enhanced water quality by reducing cyanobacteria blooms.

However, with climate change making our summers warmer and winter weather more extreme we cannot claim victory. We must continue to adapt our systems to the new weather reality and research new technologies in our effort to reduce phosphorus. This means working with the city of Lake Oswego on improving the local watershed and collaborating with organizations in the Tualatin River basin to monitor and improve our source water.

There are several ongoing projects within Oswego Lake that we are working on. We periodically post updates on these projects on our News page. Follow our efforts to improve water quality and wildlife habitat in Oswego Lake and the watershed.

Resources for Homeowners to Help Us Maintain Water Quality

Moss Control for Roofs and Decks

To maintain the quality of Oswego Lake, it’s essential to follow certain protocol when preventing and treating moss on your roof and deck.

TO PREVENT MOSS GROWTH

  • Keep roofs clean by sweeping and blowing away debris when the weather is dry.
  • Apply baking soda along the ridge line in late summer to raise the pH and deter moss growth.

TREATING EXISTING MOSS

  • Use baking soda or d-limonene-based products to treat moss.
  • Gently remove moss with a wire or nylon brush after it dies off.

AVOID THESE TREATMENT PRODUCTS

  • ZINC – Toxic to fish
  • POTASSIUM SALTS OF FATTY ACIDS – Toxic to aquatic invertebrates
  • OXIDIZING BLEACHING AGENTS WITHOUT CHLORINE – Hazardous to water due to presence of other bleaching agents, such as hydrogen peroxide, sodium percarbonate and sodium perborate.

If you do use these products, try to do so during the dry season to minimize chemical runoff. You can also disconnect downspouts during application and cleaning to allow the wash to infiltrate the soil. 

Deck Sealers and Stains

It is important to use deck sealers and stains that help keep harmful chemicals out of Oswego Lake. 

We recommend the following products:

Timber Pro Deck & Fence Formula – locally made in Portland

Eco Safety Products – Soy-based stains and sealers

About Cyanobacteria

Cyanobacteria is also called “harmful algae” although it’s not actually algae! This bacteria is found naturally in bodies of water and only become a problem when they proliferate and “bloom.” These blooms produce cyanotoxins that can be harmful to humans and pets. 

We highly recommend reading more about cyanobacteria on the Oregon Health Authority website

Current Water Quality Data

January 11, 2024

We are over half way to full, and the recent rain has really helped. The lake will connect with Lakewood Bay in the next few days and the refill rate will slow as more surface area gets connected.

Staff gauge mounted on the LOC dam. The lake is 4.5 feet from being full.

We are still only sampling in the Main Lake since the bays and canals are not accessible. What is presented below is final data from 2023, with the only thing new being samples collected from the Main Lake.

Lake Temperature

Water temperature continues to cool, but since it is currently 44 degrees it is not going to cool much more, but we may see isolated patches of ice forming this weekend as the air temperature is supposed to drop to the high teens.

Lake temperature readings at 1 meter (epilimnion) and 14 meter (hypolimnion) depths. Dark lines are the current year and light lines are last year.

Secchi

Water clarity remained steady this fall with visibility restricted by turbidity from the drawdown and a persistent algae bloom. We are shifting from cyanobacteria to diatoms so the lake will not clear up again until around May when zooplankton wake up and start eating the algae.

Secchi readings for 2023. Lake surface is represented by the top of the y-axis, with higher Secchi readings reaching deeper into the lake.

Phytoplankton biovolume in Lakewood Bay has decreased a lot since September 11. There is only five percent cyanobacteria present, with 84% of the biomass diatoms, and a 75% decrease in overall biovolume. Diatoms will be the dominant population until next summer when conditions favor cyanobacteria again. We are not collecting any more data from Lakewood Bay until we refill and the bay returns.

Lakewood Bay phytoplankton biomass. Orange line represents the total biomass from the sampling day. Only the most numerous groups are included. Grey line represents total biovolume from 2022. The faint grey line represents the total biovolume in 2022.

After decreasing in mid November our phytoplankton population is on the rise again. Fortunately it is mostly diatoms this time, which is typical for this time of year. Just today we received results from our January 8 sample and diatoms are continuing to increase and cyanobacteria is decreasing.

Main Lake phytoplankton biovolume. Orange line represents the total biovolume from the sampling day. Only the most numerous groups are included. The faint grey line represents the total biovolume in 2022.

West Bay is the only location that saw cyanobacteria biovolume increase during the September 25 sampling, but since the increase was from four to eleven percent the bay continued to be dominated by diatoms. We are not collecting any more data from West Bay until we refill and the bay returns.

West Bay phytoplankton biovolume. Orange line represents the total biovolume from the sampling day. Only the most numerous groups are included. The faint grey line represents the total biovolume in 2022. Total biovolume was 28 million on May 22, but in order to compare the volume between sites I trimmed the y-axis to match Lakewood Bay and the Main Lake.

Historical Data