This summer the USGS installed a new water-quality monitoring station on the docks at the Oregon Museum of Science and Industry (OMSI). The monitoring station provides timely information to help water managers make decisions about potential water testing, issuing and lifting HAB advisories, or to provide some assurance that the river is healthy. 

Oregon’s abundant sunshine and warm water often support cyanobacteria blooms during summer. Blooms interfere with recreation, particularly in the lower Willamette River, and impact drinking water in several parts of the state. Harmful algal blooms (HABs) occur when colonies of algae grow in large quantities and produce cyanotoxins. HABs often occur in the Ross Island Lagoon and enter the Holgate Channel and downstream Willamette River. These HABs have led to recreational advisories issued by the Oregon Health Authority due to cyanotoxins that are dangerous to humans and pets, especially those with direct contact with the water or bloom scums. And 2023 is no exception. 

The Willamette River is experiencing a revival in care and stewardship that harkens back to the late 1960s. Improvements in wastewater management and reduced sewage overflows have brought people back to the river in Portland. While risks from HABs remain, this seasonal monitor provides information to understand and perhaps manage HABs, while keeping everyone informed of river conditions during periods of bloom activity. 

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Ross Island Lagoon, a refuge for algae 

The lagoon is a human-made feature, a 120-foot-deep hole in the river, excavated for the gravel and sand used to construct many of Portland’s large buildings. Except for a small outlet, the lagoon is bordered by Ross Island, which affords some protection from winds allowing sunlight to penetrate and warm the surface waters. The sheltered lagoon is prime habitat for growing algae and cyanobacteria during summer. Little mixing occurs between the much colder bottom water (< 5 degrees C) compared with temperatures at approximately 25 degrees C at the surface. This strong temperature difference and generally higher temperatures, favor the development and growth of cyanobacteria.  

HABs aren’t the only organisms in the river the new monitoring station can inform. During some years, greater amounts of turbulence from high flows, a strong rush of snowmelt, or cloudy weather can delay HABs. These conditions are more favorable for diatoms and green algae to flourish. The beneficial algal bloom (BAB) has spurred a large population of zooplankton that helps boost productivity, a sign of a healthy aquatic ecosystem. 

Observations from July 2023

Through July 2023, based on plankton samples examined microscopically, the river supported blooms of colonial green algae and diatoms including (A) Asterionella and Fragilaria  (B) Synedra, with only minor amounts of cyanobacteria, which is consistent with chlorophyll and phycocyanin pigment values at the monitor in the Data Grapher time series plot (C):

HABs on the move 

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Cyanobacteria, including those that form HABs, use gas-filled structures to control their buoyancy and position in the water at a depth best for capture of sunlight and nutrients. During calm periods or slack tides, cyanobacteria may rise to the surface and form green or blue-green streaks and surface scums that are carried by river currents, tides, and the wind. 

Toward the end of July, the bloom exited the lagoon and moved downstream resulting in the current OHA HABs recreational advisory that extends from the Ross Island Lagoon to Cathedral Park due to the occurrence of microcystins.

The surface scums blow around like inner tubes carrying floating river goers, reaching into marinas, and fouling river beaches where public exposure may occur. The movement of a bloom out of the lagoon and into the river is aided by the tidal cycles, with ebb (outgoing) tides helping to pull them downstream. The USGS Morrison Bridge station (14211720) compliments the new station since it reports river level and velocity that can help predict the movement of blooms downstream, and upstream, depending on flows and tidal cycles.  

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New Monitoring Station - Stethoscope for the river 

This real-time monitoring station fills an important data gap by tracking the movement and type of phytoplankton in the river and provides an early warning when HABs occur. The data informs the public and management agencies about the occurrence and activity of a HAB and provides baseline data for any restoration planned for the lagoon. The water-quality monitoring station on the dock at OMSI is directly downstream from the lagoon, and positioned at the surface, where HABs congregate, and where the public is most likely to come into contact. 

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High-frequency readings taken every 15 minutes record water temperature, pH, dissolved oxygen, and the green pigment chlorophyll found in algae and plants growing in the water. Chlorophyll is associated with beneficial phytoplankton, small organisms that photosynthesize and provide energy for aquatic food webs. The monitor tracks the daily pH and dissolved oxygen swings that occur from algal photosynthesis and metabolism and can be used to gauge the activity and health of a population or bloom.  

Taken together these data provide a broad picture of the biological activity and resulting water quality and can be used by scientists and water managers to make decisions about sampling, or by the public as they look to recreate in the water. This monitor will also be useful to know when the bloom begins to decline or is gone altogether. 

"Multiple sensors provided evidence of the bloom picking up about a week prior to the initial advisory and provided some forewarning. I hope these data are also useful for understanding how this bloom finally ends." says USGS Research Hydrologist Kurt Carpenter. 

Data are available at the USGS web site and Data Grapher. The USGS Water Watch App can also be used to send alerts if phycocyanin levels begin to increase.  

What’s Next 

The USGS looks forward to working with our partners at the City of Portland, OMSI, Oregon DEQ, Portland State University, and Oregon State University, and others to advance science and our collective understanding of this dynamic river.  

Plans are underway for adoption and development of new tools and next generation animations and visualizations to portray the river like never before. The location of the monitoring station at OMSI provides a unique opportunity to educate and captivate tomorrow’s water scientists and engage the public that is increasingly interested in water-quality and aquatic ecology.  

The data from the monitoring station can help OMSI educate youth about water-quality and what drives different conditions. Data from the monitor could be used to investigate the effect of HABs on water-quality compared with conditions that favor beneficial plankton such as zooplankton that fish prey upon. This complex ecosystem, in OMSI’s back yard, awaits these budding scientists.