White River Algae TAG group reviews data

RBC | The White River Algae Technical Advisory Group (TAG) held a well-attended virtual meeting last week to review data from three studies conducted over the last year.

The White River during the 2019 algae bloom. | COURTESY PHOTO


The first data set, presented by Brian Hodges of Trout Unlimited in partnership with Tory Eyre of Colorado Parks and Wildlife (CPW) revealed information about stream temperatures in the upper White River.

Water temperature influences distribution, growth and survival of fish, bugs, and algae. The study utilized data from 20 sites in the North and South Forks of the White River down to the main stem of the river above Meeker.

Temperatures did not differ significantly between the North and South Forks of the White River. Hodges said this could indicate that temperature is “not a standalone predictor of algal growth,” since the recent algal blooms affected the North Fork but not the South.

Hodges also said stream temperatures were affected most significantly by air temperature and discharge into the river. Responding to a TAG member question about potential effects of “pond runoff” Hodges said “nothing jumped out” but did note there was some evidence of coldwater influx at various sites.

Lastly Hodges said temperatures on the upper White River “appeared to be suitable for cold water fishes,” adding that metrics were modeled around the Colorado River cutthroat trout.

Hodges said temperature data was only one “piece of the puzzle.”


Senior ecologist Jennifer Lynch of GEI consultants shared analysis of macroinvertebrates and their relation to algal blooms. Sampling and study design were done by the White River Conservation District, and GEI performed the data analysis.

Based on data collected from a total of 14 sites on the White River over three years, Lynch pointed out shifts in taxonomic composition of macroinvertebrates on the North Fork in June and July following insecticide spraying events. Similar but less pronounced shifts occurred at a site upstream of aerial insecticide spraying. Similar shifts did not occur on the South Fork.

“I kinda think with this insecticide question we’d have to have more data to know what’s really going on, but I suspect this [shift] may be more to do with cladophora (algae) than the spraying event,” said Lynch.

Lynch presented analytical findings with “caution” due to limited data collection. She ultimately recommended continuing the study for additional years with some adjustments to include more samples from early summer before cladophora growths appear.

Lynch also suggested repeating the insecticide study with some changes to allow for better differentiation of effects of aerial spraying versus the effects of algal blooms on macroinvertebrate populations.

In summary Lynch said macroinvertebrate assemblages in the White River were varied and diverse, and said “there was no sign of real impairment,” but reiterated that more data would provide a clearer picture.


The third and final presentation focused on results from an ongoing USGS study, which examined algal taxonomy, synoptic sampling results, streambed mobilization and historic streamflow records. USGS biologist Natalie Day started with an overview.

Data were collected at 20 sites distributed between the North and South Forks and the mainstem.


Algal species were broken down into broad classifications for the sake of the presentation and fell under four main categories or divisions:

  • Bacillariophyta (also known as diatoms) – Microscopic organisms, typically surrounded by a “glass box” like structure.
  • Chlorophyta – Micro and macroscopic algaes including cladophora and other filamentous algae. Note cladophora is one of the primary types of green algae visible during blooms.
  • Cryptophyta – A single celled algae that is not photosynthetic. Day noted that this type of algae was “very rare” in the river but present at a few sites.
  • Cyanobacteria – Photosynthetic microscopic algae also often called blue green algae.
One type of algal species present in the river is Cladophora, shown here with attached cocconeis sp. | COURTESY PHOTO

Diatoms and chlorophyta made up the vast majority of collected samples, with one or the other usually dominating at individual sites.

When discussing chlorophyta, Day observed that “they weren’t all cladophora” and said at least when looking at data samples from 2020, there were a variety of filamentous algae including species like stigeoclonium, spirogyra, ulothrix and others.

“These data really confirmed some of our ideas about what we know about algae taxonomy, and they challenged some of our understanding of algae in the White River,” said Day.

Compared to diatoms and chlorophyta, cyanobacteria made up a small amount of collected samples. Day said there were a few sites where they made up more than 25% including planktothrix, which occurred in slow moving or “ponded” areas of the river.

Another type of algae (didymo) known as “rock snot” was found in some areas of the river with slow moving water. “It’s known for being a hitch-hiker species so it could have come in from people’s waders or boots,” said Day.

She also briefly mentioned that it would be beneficial to have more taxonomy data during a normal “bad algae” year since data collected was only from 2020.


In October 2020, USGS employees collected discharge measurements and nutrient samples at all 20 sites. Sampling took place in the fall to minimize variations in either streamflow or nutrient concentrations caused by algal growth, irrigation or other factors.

Day pointed out that there was a decrease in flow of 20-40 CFS on the North Fork below Lost Creek, which did not fall in line with the other discharge measurements. Other noted losses of flow occurred on the mainstem above Highland Ditch, and above Coal Creek. Day said she was trying to find out if there were any active diversions happening at that time, and asked TAG members for assistance to determine if that was the case.

Nutrient measurements checked concentrations of nitrate, total nitrogen, orthophosphate and total phosphorus.

“Concentrations of nitrogen and phosphorus are higher on the North Fork than the South Fork,” said Day.

“We do see an increase in total nitrogen at White River above Curtis Creek near Meeker,” she said, adding that the increase was “not from nitrate, so it must be from organic nitrate or ammonium entering the river.”

The study also examined nutrient loads at each site, and according to Day would be further analyzed to locate potential sources of nitrogen entering the river.


Day discussed results of multiple surveys that examined streambed mobilization as a result of shear stress caused by snowmelt runoff.

“Shear stress can affect algal attachment to rocks, it can move sediment and nutrients, and can reorganize the physical habitat of the stream channel,” explained Day. She said results indicated that streambed mobilization likely occurred in 2019, but not in 2018 or 2020.

“We’re gonna take all of this information based on three years of data collection and try and make sense of why we saw really high chlorophyll in 2018, but not in 2019 and 2020,” said Day, adding, “That’s where I think this type of project lends itself to a more sophisticated modeling approach.”


Streamflows were in normal range for the first part of 2018 before dropping into the “much below normal” range in the mid and late summer, when massive algal blooms were happening. 2019 stream flows represented a drastic shift into the “much above normal” range for most of the summer thanks to high snowpack. Day noted “2019’s peak flow has a 14% chance of occurring in a given year.”

In 2020, stream flows dipped back down to “much below normal” for most of the summer.

Brian Hodges of Trout Unlimited said he was excited to see the results from further analysis of that data. He also said “we’ve known that the algae issue was bigger than cladophora and this was sort of the evidence to support that.”

USGS plans to share another update in August of this year.
Results of these studies will be made available at https://www.whiterivercd.com/white-river-algae-study.html

By LUCAS TURNER | lucas@ht1885.com