Willamette River plankton & water-quality update: May 2024

By Oregon Water Science Center May 14, 2024

See what Phytoplankton we saw in our Willamette River water samples on May 14, 2024.

USGS scientists are analyzing water samples and data from the Willamette River in the Portland area to get an idea of what types of phytoplankton, particularly toxin-producing cyanobacteria, are present and if conditions indicate an algal bloom.

Using a plankton net tow, we collected samples at the Oregon Museum of Science and Industry (OMSI) dock on May 14, 2024. Our samples show some of the main culprits of harmful algae blooms are already present (no Microcystis observed yet).

Numerically, there were more diatoms, but some cyanobacteria were present.

Organisms present on May 14, 2024:

Dolichospermum (cyanobacteria):

Large colonies with elongated spores (akinetes) and many nitrogen-fixing cells that convert nitrogen from a gas into a biologically-available form they can use for growth. Possibly toxigenic.

squiggly, spiral, cylindrical translucent green organism in light blue water — *Dolichospermum* cells can form heterocysts and akinetes. Heterocysts are specialized cells that fix nitrogen, allowing the population to survive when local nitrogen levels are low. Akinetes are thick-walled cysts that remain dormant in sediment until conditions are favorable for another bloom.

Aphanizomenon:

Starting to form colonies known as fascicles. Probably not toxigenic.

brown green straight filaments in light blue water — *Aphanizomenon* is a type of cyanobacteria often found in freshwater. Under the right conditions, it can form thick blooms. Among its different species, *Aphanizomenon flosaquae* is the most common in toxic cyanobacteria blooms.

Oscillatoria:

Within the cyanobacteria, there were more benthic filaments (bottom dwelling) compared to those living in the water column (planktonic). This Oscillatoria shows a dark band, a separation disk, which indicates the initial stages of the fragmentation / dispersal process. Possibly toxigenic.

A single translucent green threadlike organism in light blue water — *Oscillatoria* is a type of blue-green algae commonly found in freshwater. This unbranched, thread-like alga can appear alone or in tangled mats. It gets its name from its slow, rhythmic movement. It reproduces by breaking into pieces, where dead concave cells act as separation points, called separation disks, creating new filaments called hormogonia. Towards the tip of this Oscillatoria a separation disk is visible.

After May 14, 2024, there have been only minor indications of cyanobacteria in the Willamette River, but that can change if improvements in growing conditions occur.

Blue line of phycocyanin data since early May. Values stayed under 0.57 micro grams per liter — Phycocyanin data from the USGS Willamette River at Holgate Channel monitoring station. Phycocyanin is the blue-green pigment indicative of cyanobacteria and HABs. View current data.

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