U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2018–5083

Prepared in cooperation with the U.S. Army Corps of Engineers

Temporal and Spatial Monitoring of Cyanobacterial Blooms 

at Willow Creek Reservoir, North-Central Oregon
Cover: An algal surface accumulation occurring in the northwestern corner of Willow Creek Reservoir, 

north-central, Oregon, September 23, 2015, at 1009 PDT. Photograph by U.S. Geological Survey.
Temporal and Spatial Monitoring of 

Cyanobacterial Blooms at Willow Creek 

Reservoir, North-Central Oregon 

By Cassandra D. Smith

Prepared in cooperation with the U.S. Army Corps of Engineers

Scientific Investigations Report 2018–5083

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

RYAN K. ZINKE, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2018

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Suggested citation:

Smith, C.D., 2018, Temporal and spatial monitoring of cyanobacterial blooms at Willow Creek Reservoir, 

north-central Oregon: U.S. Geological Survey Scientific Investigations Report 2018–5083, 26 p., 

https://doi.org/10.3133/sir20185083.

SSN 2328-0328 (online)
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................3

Description of Study Area ..................................................................................................................3

Data Collection...............................................................................................................................................4

Northwestern Corner Continuous Water-Quality Monitoring .......................................................4

Camera Monitoring...............................................................................................................................5

Spatial Mapping ...................................................................................................................................6

Water-Quality Analyses and Data Visualization ......................................................................................8

Northwestern Corner Continuous Water-Quality Monitoring Results.........................................8

Camera Monitoring Results ..............................................................................................................12

Camera and Instrument Results.......................................................................................................15

Spatial Mapping Results....................................................................................................................15

Temporal and Spatial Monitoring of Cyanobacterial Blooms...............................................................19

Summary and Conclusions.........................................................................................................................24

Acknowledgments.......................................................................................................................................24

References Cited..........................................................................................................................................25

Figures

1. Map showing Willow Creek Reservoir near the town of Heppner, Oregon .......................4

2. Aerial image showing locations of a surveillance camera and the five camera

image positions at Willow Creek Reservoir, north-central Oregon......................................6

3. Aerial image of surface transects for mapping water quality in Willow Creek

Reservoir, north-central Oregon ................................................................................................7

4. Graph showing hourly pH and dissolved oxygen percent saturation data during

May–September 2015 at the fixed location in the northwestern corner of Willow

Creek Reservoir, north-central Oregon.....................................................................................9

5. Graph showing hourly total chlorophyll and turbidity data during May–September

2015 at the fixed location in the northwestern corner of Willow Creek Reservoir,

north-central Oregon .................................................................................................................10

6. Graph showing median, 10th–90th percentiles, and the 25th–75th percentiles for

blue-green algae―phycocyanin data collected during May–September 2015 at 

the fixed location in the northwestern corner of Willow Creek Reservoir, 

north-central Oregon .................................................................................................................11

7. Two images of a cyanobacterial bloom in Willow Creek Reservoir taken 

15 minutes apart from the same position on May 21, 2015 ..................................................12

8. Images taken by the Axis 214 camera in the northwestern corner of Willow Creek

Reservoir, north-central Oregon, showing four types of image quality.............................13

9. Images taken by the Axis 214 camera in the northwestern corner of Willow Creek

Reservoir, north-central Oregon, showing functionality of website ..................................14
iv

Figures—Continued

10. Graph showing comparison of the total chlorophyll data from the continuous

water-quality instrument and the camera images................................................................16

11. A colorized map representing relative total chlorophyll concentrations throughout

the reservoir at 1.5 feet deep on September 16, 2016, from 1150 and 1400 PDT..............17

12. A colorized map representing water temperature throughout the reservoir at 

1.5 feet deep on September 16, 2016, from 1150 to 1400 PDT..............................................18

13. A colorized map representing relative blue-green algae―phycocyanin

concentrations throughout the reservoir at 1.5 feet deep on September 16, 2016,

from 1150 and 1400 PDT.............................................................................................................19

14. An algal surface accumulation occurring in the northwestern corner of Willow

Creek Reservoir, north-central, Oregon, November 7, 2016, at 1223 PST .........................20

15. An algal bloom occurring along the dam face in Willow Creek Reservoir,

north-central Oregon, September 26, 2016, at 1150 PDT......................................................21

16. An algal surface accumulation occurring in the northwestern corner of Willow

Creek Reservoir, north-central Oregon, September 28, 2016, at 1048 PDT .......................22

17. A boat paddles through an algal bloom occurring in the northwestern corner of

Willow Creek Reservoir, north-central Oregon, October 10, 2016, at 1109 PDT...............23

Tables

1. Descriptions of type of equipment, type of data collected, and dates of data

collection during 2015 and 2016 field seasons at Willow Creek Reservoir,

north-central Oregon ..................................................................................................................5

2. Comparison of the YSI EXO2 multi-parameter water-quality readings measured 

at the same location in Willow Creek Reservoir, north-central Oregon, 

June 9, 2015 ................................................................................................................................15
v

Conversion Factors 

U.S. customary units to International System of Units

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2

)

acre 0.4047 hectare (ha)

acre 0.4047 square hectometer (hm2

) 

acre 0.004047 square kilometer (km2

)

Volume

acre-foot (acre-ft) 1,233 cubic meter (m3

)

acre-foot (acre-ft) 0.001233 cubic hectometer (hm3

) 

Speed

mile per hour (mi/h) 1.609 kilometer per hour (km/h)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 × °C) + 32.

Datum

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Supplemental Information

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius 

(μS/cm at 25 °C).

Concentrations of chemical constituents in water are given in either milligrams per liter (mg/L) 

or micrograms per liter (μg/L).

Temporal and Spatial Monitoring of Cyanobacterial 

Blooms at Willow Creek Reservoir, North-Central Oregon 

By Cassandra D. Smith

Abstract

The U.S. Geological Survey (USGS) and U.S. Army 

Corps of Engineers (USACE) investigated the spatial and 

temporal dynamics of cyanobacterial (blue-green algal) 

blooms in Willow Creek Reservoir in north-central Oregon 

in 2015–16. A combination of cameras and water-quality 

monitoring equipment was used to assess the frequency 

and duration of blooms and their effects on water quality. A 

surveillance camera captured color images every 15 minutes 

during daylight hours of the northwestern corner of Willow 

Creek Reservoir, where surface blooms tend to accumulate 

due to the prevailing summer winds. In 2015, a water-quality 

instrument was deployed in the northwestern corner of the 

reservoir to continuously measure water temperature, pH, 

dissolved oxygen, specific conductance, turbidity, total 

chlorophyll, and the blue-green algae pigment phycocyanin. 

In 2016, a water-quality instrument was used to collect 

measurements along transects throughout the reservoir to 

create spatial maps of water quality. The spatially integrated 

mapping process was repeated on three different days under 

varying algal conditions. Also in 2016, a telemetry connection 

was established allowing resource managers to view the 

reservoir images in near-real time. 

Results from 2015 indicate that surface accumulations 

of cyanobacteria can form and dissipate within minutes in the 

reservoir, and that blooms can cause substantial changes to 

water quality. A persistent cyanobacterial bloom in August and 

September 2015 resulted in pH values of 9.5 standard units, 

220 percent oxygen saturation, and pronounced increases in 

turbidity and total chlorophyll. The stationary water-quality 

instrument collected data during periods with and without 

blooms, increasing our understanding of the effects of 

blooms on water quality and revealing potential restoration 

benchmarks for the freshwater reservoir. The spatially 

integrated mapping data showed the variation in water quality 

across the reservoir that occurs during blooms and baseline 

conditions and indicated regions of the reservoir to focus 

restoration efforts. Additional spatial data collection can be 

timed to collect daily extremes. 

The camera deployment in 2016 demonstrated that 

telemetering images from remote sites is possible and 

provides valuable and timely information. Monitoring with a 

surveillance camera is inexpensive and supplies data regarding 

surface-bloom presence or absence. The use of a camera can 

help target site visits to periods when blooms are observed, 

which may increase the accuracy of beginning and ending 

dates for water body closures. 

Monitoring cyanobacterial blooms in Willow 

Creek Reservoir with multiple devices provided a more 

comprehensive dataset than any one monitoring method. 

The camera images showed when a surface bloom initiated 

and dissipated while the water-quality instrument revealed 

the magnitude, or potential severity, of the effects on water 

quality. 

Introduction

Cyanobacteria, also known as blue-green algae, are 

photosynthetic bacteria that are ubiquitous in aquatic 

ecosystems around the world (Falconer and Humpage, 

2005). When exposed to ideal conditions, cyanobacteria can 

proliferate and form blooms, which can be defined by high cell 

densities, visible surface accumulations (appearing as green 

scum), or by the dominance of a single or few species. In this 
2 Temporal and Spatial Monitoring of Cyanobacterial Blooms at Willow Creek Reservoir, North-Central Oregon

report, the term “bloom” is used to refer to high algal biomass 

or the resulting surface scums or accumulations. Blooms affect 

ecosystem health by altering food webs and causing hypoxia 

(Paerl and others, 2011). Some genera of cyanobacteria 

have the capacity to produce toxins that can cause animal 

deaths and acute and chronic human health issues (Falconer, 

1991; Carmichael and others, 2001; Chen and others, 2009). 

Cyanobacterial blooms are not always toxin-producing 

(Vézie and others, 1998), but blooms indicate the potential 

for an abundance of organisms with the ability to produce 

cyanotoxins (Graham and others, 2009). Cyanobacterial 

harmful algal blooms, commonly referred to as CyanoHABs, 

negatively impact the economy by increasing water treatment 

costs at drinking water intakes and through the loss of 

recreational revenue due to water body closures and aesthetics 

(U.S. Environmental Protection Agency, 2015). 

Factors that influence cyanobacterial blooms include 

temperature, nutrient availability, wind/mixing, water 

chemistry, and site-specific traits (Chorus and Bartram, 

1999; Briand and others, 2003; Anderson and others, 2012; 

Van der Merwe and Price, 2015). The combination of those 

factors will affect the temporal and spatial characteristics of 

the bloom (Anderson and others, 2012). Water bodies with 

warm, eutrophic water experiencing calm weather may have 

intense or prolonged blooms (Kanoshina and others, 2003), 

especially if cyanobacterial blooms have occurred in that 

water body in the past. Specific cyanobacterial cells (known 

as akinetes) can persist from year to year, making it difficult 

to break the seasonal bloom trend (Falconer and Humpage, 

2005). Population growth and increased nutrient runoff, 

coupled with warmer temperatures, may cause an increase in 

the frequency and duration of cyanobacterial blooms in the 

future. 

The U.S. Environmental Protection Agency (EPA) 

established recreational guidelines for cyanotoxins, which 

recommend that swimming advisories be posted if microcystin 

and cylindrospermopsin concentrations exceed 4 and 8 μg/L, 

respectively (U.S. Environmental Protection Agency, 2017). 

Technology is rapidly evolving in this field, but at the present 

time, inexpensive and reliable sensors that can be deployed 

to detect cyanotoxins are not available. Collecting discrete 

samples for toxins, cell count, and taxonomic identification 

is currently the most common way to identify a HAB and to 

issue an advisory or water body closure (Graham and others, 

2009). The Oregon Health Authority (2016) recommends that 

samples are collected when temperatures are warm and from 

locations where humans and animals would likely contact 

the water. In States that do not receive Federal funding for 

toxin sampling, the ability to sample the impaired water body 

and to post closures depends on management decisions in 

allocation of State resources. Toxin sampling can be costly 

and time-intensive, as many water bodies used for recreation 

are in remote areas. Therefore, discrete toxin sampling is often 

infrequent (for example, biweekly) or does not occur.

Recent monitoring techniques have utilized satellite 

imagery to detect algal biomass occurrence, spatial extent, and 

trends (Stumpf, 2001; Urquhart and others, 2017). Satellite 

sensors that distinguish cyanobacterial wavelengths and are 

available to the public (such as the European Space Agency’s 

MERIS) can be valuable tools. However, satellite monitoring 

can be inconclusive or problematic due to satellite flyover 

intervals, cloud cover, or imagery resolution. Remote sensing 

using a coarse resolution (ex: Landsat 8 with 30-m pixels) can 

obscure finer scale spatial trends in bloom occurrence, and this 

problem is compounded with smaller water bodies. There is 

a need to develop a monitoring approach that is inexpensive, 

high frequency (to characterize algal biomass dynamics), and 

can be implemented in remote water bodies of all sizes. 

Deploying a color surveillance camera is one monitoring 

method that can address the problems of infrequent site visits 

and the resolution and periodicity of remote imagery flyovers. 

Programmable color surveillance cameras with appropriate 

lenses and pan/tilt/zoom capabilities take pictures at multiple 

angles and can save them locally, as well as transmit them via 

cellular connection. These images could indicate the presence 

of a surface bloom, and short image intervals would show 

the onset, duration, and dissipation. Continuously monitoring 

water chemistry could also provide timely indications that a 

bloom is occurring. A continuous water-quality instrument 

can measure temperature, pH, dissolved oxygen, specific 

conductance, turbidity, total chlorophyll, and blue-green 

algae―phycocyanin (BGA-PC; a pigment specific to 

cyanobacteria) parameters to both confirm the imagery and 

provide the physicochemical context for the occurrence of the 

blooms. 

Some water-quality parameters can influence 

cyanobacterial blooms, and multiple parameters are affected 

by blooms. Growth rates of cyanobacteria increase in warm 

water temperatures (Johnk and others, 2008), and monitoring 

water temperature data may indicate when high algal biomass 

is likely to occur. Cyanobacteria photosynthesize and respire 

in the presence of light but only respire in the absence of 

sunlight. Photosynthesis and respiration rates result in daily 

cycles in dissolved oxygen concentrations and pH, and 

the presence of a bloom often increases the magnitude and 

the variation of the daily data (Maberly, 1996; Staehr and 

others, 2010). Biological activity including photosynthesis 

and respiration can affect the percent oxygen saturation, 

and high algal biomass can result in readings greater than 

100 percent while algal die-offs may result in hypoxic and 

anoxic conditions. 
Introduction 3

Discharge and runoff events transport suspended 

sediment and nutrients (nitrogen and phosphorus) that can 

promote bloom occurrence. Turbidity is an optical property 

of water that is influenced by suspended particles and 

dissolved compounds (Wagner and others, 2006). While 

turbidity sensors effectively measure the light-scattering 

effects of fine, reflective particles in the water column, algal 

filaments and colonies also may be detected (Sadar, 1998). 

Algal and cyanobacterial blooms with high cell densities 

can increase turbidity in a water body (Paerl and Huisman, 

2008), and water-quality data can reflect a positive correlation 

with turbidity and cyanobacteria abundance. Chlorophyll 

concentrations increase as photosynthetic biomass (green 

algae and blue-green algae) increases, and BGA-PC increases 

as cyanobacteria abundance increases. Monitoring chlorophyll 

and BGA-PC fluorescence shows relative patterns when 

cyanobacteria are proliferating and decreasing. 

Willow Creek Reservoir is a recreational destination in 

Oregon that is affected by frequent CyanoHABs during the 

summer (Harris and others, 2014). Due to the remote location 

of the reservoir, a monitoring technique that minimizes site 

visits and provides near-real time information would assist 

in decision-making about water body safety and closures. 

This report describes a proof-of-concept monitoring study 

conducted at Willow Creek Reservoir that used existing 

camera technology and water-quality instrumentation and 

tested the utility of information provided to the resource 

managers.

Purpose and Scope

This research was conducted to (1) evaluate multiple 

monitoring devices and data collection methodology, 

(2) establish an early warning system of cyanobacterial 

blooms, and (3) to increase our understanding of 

cyanobacterial blooms in Willow Creek Reservoir by 

monitoring the effects of cyanobacterial blooms on the 

reservoir’s water quality. This report documents the data 

collected by USGS from Willow Creek Reservoir in 2015 

and 2016 and draws conclusions regarding the utility of the 

various monitoring devices, including the circumstances under 

which they may be most applicable to other water bodies that 

tend to produce cyanobacterial blooms. 

Description of Study Area 

Willow Creek Reservoir is in north-central Oregon 

within Morrow County and near the town of Heppner 

(fig. 1). Heppner, Oregon, is in the U.S. EPA-designated 

Columbia Plateau ecoregion, and specifically in the Umatilla 

Plateau ecoregion. This region is characterized by a plateau 

of Columbia River Basalt, few trees, and loess deposits of 

varying thickness that are farmed. The area surrounding the 

reservoir includes numerous farms that primarily cultivate 

wheat. 

Willow Creek Dam was built in 1983 by the USACE for 

flood risk reduction, and the dam impounds Willow Creek 

and Balm Fork Creek to create Willow Creek Reservoir. The 

125-acre reservoir can hold a maximum of 13,250 acre-ft 

of water, and USGS operates streamgages (U.S. Geological 

Survey, 2018a) on an incoming tributary (streamgage No. 

14034470), the outflow from the dam (streamgage No. 

14034500), and historically operated a stream gage on the 

other incoming tributary (streamgage No. 14034480). 

Willow Creek Reservoir contains high total phosphorus 

concentrations, potentially due to high phosphorus 

concentrations in the basalt parent material (Abrams and 

Jarrell, 1995; Porder and Ramachandran, 2012), and has 

been studied and managed for its frequent cyanobacterial 

blooms. Water samples collected from 1984 to 1996 were 

examined by Aquatic Analysts, Incorporated (Larson, 

1997). Six genera of cyanobacteria were identified including 

Dolichospermum sp. (formerly Anabaena), Aphanizomenon 

sp., Chroococcus sp., Gloeotrichia sp., Microcystis sp., and 

Oscillatoria sp. (Larson, 1997). The cyanobacterial blooms 

are a concern to resource managers and toxin sampling 

began in the reservoir in 2006 (Harris and others, 2014). The 

dominant genus of cyanobacteria during the 2015 and 2016 

bloom seasons was Dolichospermum (formerly Anabaena) 

or Aphanizomenon, and Green Water Laboratories (Palatka, 

Florida) documented a shift in the planktonic community from 

dominance of Dolichospermum in May 2015 to dominance of 

Aphanizomenon in October 2015 (Green Water Laboratories, 

unpub. data). Due to the prevailing winds at Willow 

Creek Reservoir, any cyanobacterial surface scums tend to 

accumulate in the northwestern corner of the reservoir against 

the dam.

In addition to the routine toxin sampling, multiple studies 

have been conducted in the reservoir to increase understanding 

of the system and to experiment with mitigation techniques. 

Researchers constructed large mesocosms in the reservoir and 

manipulated the total nitrogen to total phosphorus (TN:TP) 

ratio. Results indicated that adding ammonium nitrate (to 

increase the TN:TP) decreased cyanobacteria abundance and 

toxin concentration while increasing water clarity (Harris 

and others, 2014). One study experimented with nutrient 

removal by deploying solar-powered water-circulating devices 

in Willow Creek Reservoir, and current research involves 

quantifying the phosphorus flux into the reservoir through 

sediments (Frank Wilhelm and Sarah Burnet, University of 

Idaho, unpub. data).
4 Temporal and Spatial Monitoring of Cyanobacterial Blooms at Willow Creek Reservoir, North-Central Oregon

tac18-1227_fig 01

Heppner

Willow

Creek

Willow

Creek

Willow Creek

Balm Fork

Shobe Creek Shobe Creek

Willow Creek Reservoir

14034470

14034480

14034500

OREGON

MORROW

COUNTY

Map

area

119°33'30" 119°33' 119°32'30" 119°32' 119°31'30" 119°31'

45°

21'

45°

20'

30"

45°

20'

0 0.2 0.4 0.6 0.8

0.2 0.4 0.6 0.8

1.0 MILES

0 1.0 KILOMETERS

Base image from Esri, copyright, 2018. Coordinate reference system: NAD83 

UTM Zone 10N. Horizontal datum is North American Datum of 1983.

14034480

EXPLANATION

U.S. Geological Survey 

streamgage and No.

Figure 1. Willow Creek Reservoir near the town of Heppner, Oregon.

Data Collection

Multi-parameter water-quality instruments and a color 

surveillance camera were used to collect data regarding algal 

conditions (table 1). 

Northwestern Corner Continuous Water-Quality 

Monitoring

A Yellow Springs Instrument (YSI) EXO2 waterquality instrument with probes for seven parameters 

(water temperature, specific conductance, pH, dissolved 

oxygen, turbidity, total chlorophyll, and blue-green algae―

phycocyanin) was programmed to log internally and hourly. 

The water-quality instrument was housed in a 3-ft segment of 

PVC pipe, and 1-inch holes were liberally drilled throughout 

the pipe to allow free-flowing water to the probes. The PVC 

housing was attached to buoys and was positioned to remain 

horizontal with the probes 1.5 ft (0.5 m) below the surface of 

the water. Chain and concrete anchors were used to keep the 

instrument in place; the instrument continued to measure water 

generally in the same location as the water level declined 

throughout the summer season and the extra slack in the chain 

allowed the instrument to slightly migrate from the original 

location. The instrument was deployed in the northwestern 

corner of the reservoir where surface blooms accumulate, 

approximately 75 ft from the dam, and directly across from the 

camera on the dam. 
Data Collection 5

Table 1. Descriptions of type of equipment, type of data collected, and dates of data collection during 2015 and 2016 field seasons at 

Willow Creek Reservoir, north-central Oregon.

[YSI, Yellow Springs Instrument]

Type of equipment Type of data collected Dates of data collection

YSI EXO2 multi-parameter waterquality instrumentContinuous (hourly) water-quality data from one 

location in the northwestern corner of the reservoir.

May 13 to Sept. 21, 2015

Axis 214 color surveillance camera Five images of the northwestern corner of the reservoir 

every 15 minutes during daylight hours.

May 14 to Nov. 9, 2015 (not telemetered)

July 20 to Nov. 22, 2016 (telemetered)

YSI EXO2 multi-parameter waterquality instrumentSpatial water-quality data throughout the reservoir. June 9, 2015; Aug. 17, 2016; Sept. 16, 2016

A clean and calibrated instrument was deployed on 

May 13, 2015 and monthly site visits were conducted 

following standard USGS protocols (Wagner and others, 

2006). At each site visit, the instrument was cleaned and 

then swapped with a newly calibrated EXO2. During site 

visits, a wide-mouth 1-L polypropylene bottle was inverted 

in the water next to the instrument probes (1.5 ft deep) and 

filled, taking care to avoid the collection of any surface 

scum. The sample water was added to an 8-L polyethylene 

churn sample splitter (Wilde and others, 2004), and this 

process was repeated until the churn sample splitter contained 

approximately 6 L of water. The EXO2 water-quality 

instrument was positioned in the churn sample splitter, and 

multiple total chlorophyll readings were logged and averaged. 

The composite water sample was homogenized using the 

churn paddle and two 1-L subsamples were dispensed from 

the spigot. The samples were filtered, frozen, and analyzed 

at the USGS Oregon Water Science Center using a Trilogy®

Laboratory Fluorometer and following EPA Method 445.0 

In Vitro Determination of Chlorophyll a (Arar and Collins, 

1997). 

Following site visits, the internally logged instrument 

data were downloaded and the appropriate fouling and 

calibration corrections were applied to the data (Wagner and 

other, 2006). Calibration corrections to the total chlorophyll 

record were based on the laboratory readings. All continuous 

water-quality data are available online in the National Water 

Information System as site 452053119323001 Willow Creek 

Reservoir NW Corner, OR (U.S. Geological Survey, 2018a).

Camera Monitoring

A camera was deployed to observe cyanobacterial 

surface blooms occurring in Willow Creek Reservoir. An Axis 

214 color surveillance camera was chosen for this proofof-concept study because it had the ability to pan, tilt, and 

zoom, and was programmable. Additionally, the camera could 

withstand hot temperatures, could be fitted with a polarizing 

lens to potentially reduce glare, and was able to either store 

images internally or connect to a wireless network to transmit 

images. 

The camera was positioned above the water and facing 

downwards to achieve the desired contrast in colors. The 

camera was attached to a railing of the Willow Creek Dam in 

the northwestern corner of the reservoir about 70 ft above the 

surface of the water. The system was powered by a solar panel 

and large battery, and the camera was programmed to take a 

series of five pictures every 15 minutes during daylight hours 

(fig. 2). 

During 2015, the camera was installed on May 14 and 

retrieved on November 9. Site visits occurred at regular 

intervals and consisted of downloading the stored images and 

troubleshooting any issues. A polarizing lens specific to the 

Axis 214 camera was tested from May to July 2015. 

The camera was installed at the same location on July 20, 

2016, and was retrieved November 22, 2016. Site visits were 

frequent and multiple modems, antenna, and cellular phone 

companies were tested to attain consistent telemetry of the 

images. A script was created that uploaded the telemetered 

images to a public website in near-real time. 
6 Temporal and Spatial Monitoring of Cyanobacterial Blooms at Willow Creek Reservoir, North-Central Oregon

tac18-1227_fig 02

Willow Creek

Reservoir 1

2

3

4

5

Background image from Google, copyright, 2018. 0 100 200 FEET

0 25 50 METERS

Figure 2. Locations of a surveillance camera and the five camera image positions at Willow Creek Reservoir, north-central Oregon. 

The location of the camera on the dam is indicated by the five-pointed star, and the numbered rectangles indicate the approximate area 

captured by each camera image. Position number 1 is photographed first, followed by position number 2, and in order through position 

number 5. The yellow circle represents the approximate location of the continuous water-quality instrument. Background image is from 

Google (https://www.google.com/maps/place/Heppner,+OR+97836/@45.3476167,-119.5439632,409m/data=!3m1!1e3!4m5!3m4!1s0x54bcde

9fefa0ff5f:0x8c43eb5baecaeb35!8m2!3d45.3531842!4d-119.5577997, accessed December 21, 2017).

Spatial Mapping 

Surface water in Willow Creek Reservoir was mapped 

along transects using a water-quality instrument three times 

in 2015–16. A YSI EXO2 multi-parameter instrument was 

outfitted to measure seven parameters (water temperature, 

specific conductance, pH, dissolved oxygen, turbidity, total 

chlorophyll, and BGA-PC) and programmed to log internally 

every 10 seconds. The weighted, calibrated YSI EXO2 multiparameter instrument was attached to a boat cleat on the right 

side at the front of the boat. The boat began data collection at 

the southern end of the reservoir near location 5 (fig. 3) and 

progressed about 2.5 mi/h throughout the reservoir; the speed 

was chosen to ensure the probes remained submerged 1.5 ft 

below the surface. A tablet or Trimble GPS unit recorded 

the GPS track and logged readings every 3 seconds. The 

boat roughly followed the GPS track (fig. 3) and traversed 

the reservoir without pausing, ending at the eastern end of 

the reservoir near location 1. After the track was completed, 

discrete chlorophyll-a samples were collected at the accessible 

locations (1–5); samples were analyzed at the Oregon Water 

Science Center following the procedures listed above to 

compare to the instrument measurements. 
Data Collection 7

tac18-1227_fig 03

Willow

Creek

Reservoir

Willow Creek Arm

Balm Fork Arm

Background image from Google, copyright, 2018. 0 1,000 FEET

0 250 METERS

Figure 3. Surface transects for mapping water quality in Willow Creek Reservoir, north-central Oregon. The white line denotes 

the approximate GPS path the boat followed while logging water-quality parameters with a Yellow Springs Instrument (YSI) EXO2 

instrument. The boat returned to locations 1–5 and collected discrete chlorophyll-a water samples. A stationary, continuous instrument 

was located at location 3 and a surveillance camera location is symbolized by the white marker with a black star. Willow Creek flows 

into the reservoir from the east and Balm Fork Creek flows into the reservoir from the south.
8 Temporal and Spatial Monitoring of Cyanobacterial Blooms at Willow Creek Reservoir, North-Central Oregon

Water-Quality Analyses and Data 

Visualization 

Northwestern Corner Continuous Water-Quality 

Monitoring Results

The water-quality instrument measured high frequency 

data from one location in the reservoir, often where the 

cyanobacterial surface blooms accumulate. Collecting 

continuous water-quality data from a bloom-prone location 

can reveal how the water quality is affected by cyanobacterial 

blooms. Water temperature ranged from 15.0 °C on May 14, 

2015 to 26.6 °C on July 2, 2015 and often experienced diel 

fluctuations of 1 °C or less. Specific conductance generally 

increased from May 2015 to early September 2015, with a 

minimum of 211 μS/cm and a maximum of 252 μS/cm. On 

59 days during May, August, and September 2015, the pH 

was greater than or equal to 9.0 standard units and reached a 

maximum of 9.5 standard units on September 11, 2015 (fig. 4). 

The percent oxygen saturation at Willow Creek Reservoir 

was greater than 100 percent for most of the deployment 

period, and neither anoxic nor hypoxic concentrations 

were measured at this near-surface location. In September, 

dissolved oxygen reached 220.5 percent saturation (fig. 4). 

Turbidity, total chlorophyll, and BGA-PC data have similar 

trends with pronounced variation and elevated measurements 

during the May and August/September blooms (fig. 5). Total 

chlorophyll readings ranged from 0.5 to 115.0 μg/L, and 

based on the total chlorophyll concentrations, the reservoir 

likely shifted to eutrophic and hypereutrophic states during 

May and August/September (Carlson and Simpson, 1996). 

The laboratory-corrected total chlorophyll concentrations may 

differ from actual values between sample collection dates 

due to the complexity of phytoplankton communities and the 

many factors affecting chlorophyll fluorescence. BGA-PC 

reached a minimum of 0 and maximum of 20.8 μg/L during 

the deployment (fig. 6); however, the BGA-PC data were 

not corrected to discrete samples and values are considered 

relative concentrations. 

The instrument data from this study show periods of 

high algal productivity (characterized by elevated pH and 

dissolved oxygen) during May, August, and September 2015. 

The data show that the percent oxygen saturation at Willow 

Creek Reservoir was greater than 100 percent saturation 

throughout most of the study period, which indicates that 

photosynthesizing organisms in the water column were 

producing and releasing oxygen. Other optical parameters 

including the total chlorophyll, turbidity, and BGA-PC also 

indicated that the water quality was affected in May, August, 

and September. Specific conductance data decreased for a few 

days in mid-September, which corresponds to the elevated pH, 

dissolved oxygen, total chlorophyll, turbidity, and BGA-PC 

readings. The water was super-saturated with oxygen and 

it is possible that air bubbles accumulated in the specific 

conductance probe, decreasing the readings during that time 

period.
Water-Quality Analyses and Data Visualization 9

tac18-1227_fig 04

80

95

110

125

140

155

170

185

200

215

230

Oxygen saturation, in percent

8.6

8.7

8.8

8.9

9.0

9.1

9.2

9.3

9.4

9.5

9.6

pH, in standard units

Willow Creek Reservoir NW Corner, OR (452053119323001)

May June July

2015

August September

15 1 15 1 15 1 15 1 15

Figure 4. Hourly pH (standard units) and dissolved oxygen percent saturation data during May–September 2015 at the fixed 

location in the northwestern corner of Willow Creek Reservoir, north-central Oregon. Oxygen percent saturation values were 

calculated using algorithms from USGS Data Grapher (U.S. Geological Survey, 2018b).
10 Temporal and Spatial Monitoring of Cyanobacterial Blooms at Willow Creek Reservoir, North-Central Oregon

tac18-1227_fig 05

Willow Creek Reservoir NW Corner, OR (452053119323001)

May June July

2015

August September

15 1 15 1 15 1 15 1 15

0

5

10

15

20

25

30

35

40

45

50

55

60

Turbidity, in Formazin Nephelometric Units (FNU)

0

10

20

30

40

50

60

70

80

90

100

110

120

Total chlorophyll, in micrograms per liter 

Figure 5. Hourly total chlorophyll (μg/L) and turbidity (FNU) data during May–September 2015 at the fixed location in the 

northwestern corner of Willow Creek Reservoir, north-central Oregon (U.S. Geological Survey, 2018b).
Water-Quality Analyses and Data Visualization 11

tac18-1227_fig 06

10th–90th percentile

25th–75th percentile

Median

EXPLANATION

Willow Creek Reservoir NW Corner, OR (452053119323001)

May June July

2015

August September

15 1 15 1 15 1 15 1 15

0

1

2

3

4

5

6

7

8

9

10

11

12

13

Phycocyanin, in micrograms per liter

Figure 6. Median, 10th–90th percentiles, and the 25th–75th percentiles for blue-green algae―phycocyanin data 

collected during May–September 2015 at the fixed location in the northwestern corner of Willow Creek Reservoir, 

north-central Oregon (U.S. Geological Survey, 2018b).
12 Temporal and Spatial Monitoring of Cyanobacterial Blooms at Willow Creek Reservoir, North-Central Oregon

Camera Monitoring Results

All camera images from 2015 and 2016 are archived 

in Smith (2017a). Monitoring surface blooms with a camera 

revealed that surface accumulations in this reservoir have 

the capacity to form and dissipate within 15 minutes based 

on wind and currents (fig. 7). In 2015, the camera was 

functioning and saved images on 106 of 180 days that the 

camera was deployed. The 74 days of missing images were a 

result of technical issues caused by faulty charge controllers 

for the solar panel. During the 2016 deployment, images 

were telemetered on 108 of 126 days. The 18 days of missing 

images were due to poor cellular coverage; consistent 

telemetry began in September 2016 when the cellular 

company, modem, and antenna were replaced. 

The proof-of-concept camera monitoring study 

demonstrated that cyanobacterial surface blooms were visible 

in images from a color surveillance camera. Successive 

images could be joined together to view a video of the bloom 

on a given day. Not all images were clear or useful, and 

figure 8 shows a variety of images from the 2015 and 2016 

field seasons. The use of a polarizing lens during this study 

was unnecessary and caused the cyanobacterial blooms to 

appear light brown. Collecting high-frequency images was 

advantageous considering that some images were obscured by 

glare or cloud reflection. Telemetering images from Willow 

Creek Reservoir was successful, and images could be viewed 

in near-real time by the resource managers (fig. 9).

Figure 7. Two images of a cyanobacterial bloom in Willow Creek Reservoir taken 15 minutes apart from the same position on May 21, 

2015. The image on the left shows a surface accumulation, which is the lighter color and covering about three-quarters of the image. 

The image on the right shows the bloom mixed in the water. The blooms appear brown because the camera was temporarily outfitted 

with a polarizing lens. Photographs by U.S. Geological Survey.
Water-Quality Analyses and Data Visualization 13

tac18-1227_fig 08

Polarizing lens Reflection

Glare Desired outcome

Figure 8. Images taken by the Axis 214 camera in the northwestern corner of Willow Creek Reservoir, north-central Oregon, showing 

four types of image quality. The top left panel shows a complete covering of a cyanobacterial surface scum that appears brown due 

to the polarizing lens. The top right panel and the bottom left panel are examples of interference from cloud reflection and glare. The 

bottom right image captures a cyanobacterial bloom in the northwestern corner of the reservoir without the use of a polarizing lens. 

Photographs by U.S. Geological Survey.
14 Temporal and Spatial Monitoring of Cyanobacterial Blooms at Willow Creek Reservoir, North-Central Oregon

tac18-1227_fig 09

Figure 9. Images taken by the Axis 214 camera in the northwestern corner of Willow Creek Reservoir, north-central Oregon, showing 

functionality of website. Images of the surface of the water were taken at five positions every 15 minutes during daylight hours. 

During 2016, the images were telemetered to a website in near real-time. This figure displays the functionality of the website that was 

available to both researchers and resource managers.
Water-Quality Analyses and Data Visualization 15

Camera and Instrument Results

Comparing the camera and water-quality instrument 

results indicated that the findings generally supported each 

other, but that differences in surface and water column 

conditions did occur. Images from May 14 through June 26, 

2015, were visually inspected for the presence of a surface 

bloom accumulation, and camera images showed surface 

blooms during a total of 200 daylight hours of that period. The 

continuous water-quality data were collected from 1.5 ft below 

the surface of the water, and figure 10 displays the hourly 

visual bloom occurrences overlaid with the continuous total 

chlorophyll data from the same period. 

The elevated total chlorophyll data indicated when bloom 

conditions were measured with the water-quality instrument. 

Similar trends and timing were observed in the pH, dissolved 

oxygen, turbidity, and BGA-PC data. There were a few hours 

in June where surface accumulations were observed in images, 

but no elevated response was detected by the total chlorophyll 

probe (fig. 10). The ephemeral surface accumulations observed 

on June 14, June 21, and June 26, 2015, appeared in the early 

morning; it is possible that those films were not comprised 

of cyanobacteria and were possibly pollen. Conversely, 

the water-quality instrument measured relatively high total 

chlorophyll in early June that was not detected by the camera. 

Spatial Mapping Results

All data from the three spatial mapping events are 

archived in Smith (2017b). A period of low algal activity 

was observed during the mapping event conducted from 

1103 to 1245 PDT on June 9, 2015; the LandSat 8 image and 

the color surveillance camera images (not shown) confirm 

that the reservoir did not have high algal productivity or a 

cyanobacterial surface accumulation at that time. Dissolvedoxygen measurements ranged from 109.2 to 115.0 percent 

saturation, and the EXO2 total chlorophyll readings ranged 

from 0.4 to 1.2 μg/L. The stationary, continuous water-quality 

instrument logged similar readings as were collected from the 

mapping effort (table 2). 

During the mapping event on August 17, 2016 (from 

1305 to 1430 PDT), water appeared green and possible 

Aphanizomenon filaments were observed, but no surface 

bloom was present. Dissolved-oxygen measurements reached 

155.8 percent saturation and pH reached 9.15 standard units, 

which are indicative of high levels of algal activity. Most 

of the total chlorophyll readings were low (< 1 μg/L), but 

elevated total chlorophyll readings (maximum of 34.8 μg/L) 

were detected in a small area in the Balm Fork arm of the 

reservoir. 

Table 2. Comparison of the YSI EXO2 multi-parameter water-quality readings measured at the same 

location in Willow Creek Reservoir, north-central Oregon, June 9, 2015.

[Instrument readings: Stationary, continuous instrument logged hourly, while the spatial mapping instrument was secured 

to a moving boat and logged every 10 seconds. Both instruments were 1.5 feet (0.5 meter) below the surface of the water. 

Total chlorophyll values are raw values, not corrected to discrete samples. YSI, Yellow Spring Instrument]

Parameter

Instrument readings

Spatial mapping

(recorded at 1140 PDT)

Stationary, continuous

(recorded at 1200 PDT)

Water temperature (degrees Celsius) 24.23 24.02

Specific conductance (microsiemens per centimeter) 229.6 228.0

pH (standard units) 8.93 8.93

Dissolved oxygen (milligrams per liter) 9.17 9.40

Turbidity (Formazin Nephlometric Units) 0.52 0.60

Chlorophyll, total (micrograms per liter) 0.49 0.48

Blue-green algae–phycocyanin (micrograms per liter) 0.12 0.11
16 Temporal and Spatial Monitoring of Cyanobacterial Blooms at Willow Creek Reservoir, North-Central Oregon

tac18-1227_fig 10

Surface accumulation visible in imagesNo photo (either night or missing)Surface accumulation not present in imagesTotal chlorophyll

EXPLANATION

2015

May June

Total chlorophyll, in micrograms per liter

14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

50

40353025201510

Figure 10. Comparison of the total chlorophyll data from the continuous water-quality instrument and the camera images. The total chlorophyll data are comprised 

of hourly readings that were measured in micrograms per liter and adjusted to discrete laboratory values. All surface water images from all locations were visually inspected for this period. Light green bars indicate that a surface bloom was visible in the images. The white areas (lack of colored bars) represent the hours when images were collected, but surface blooms were not observed. The camera did not capture images between late evening and early morning, and the gray regions were a result of the camera being off at night or missing images (June 9, 2015). 
Water-Quality Analyses and Data Visualization 17

A surface bloom was present in the northwestern corner 

of the reservoir during the mapping event that took place 

from 1150 to 1400 PDT on September 16, 2016. Measured 

dissolved oxygen reached a maximum of 121.6 percent 

saturation while total chlorophyll readings reached a 

maximum of 4.9 μg/L (fig. 11). Instrument readings were 

assigned to the closest corresponding GPS coordinate reading 

in time. Data were analyzed in ArcGIS using the Inverse 

Distance Weighted spatial analyst tool to create colorized 

maps that represent how the water quality varied spatially in 

the reservoir. A water temperature map from September 16, 

2016 (fig. 12) reveals warmer water along the southern edges 

of the reservoir (within the Balm Fork arm) and along the 

face of the dam. The dissolved oxygen map from that date 

shows higher oxygen percent saturation in areas with warmer 

temperatures, indicating that more algal productivity is 

occurring in these areas. The total chlorophyll and BGA-PC 

trends provided supporting evidence for what was observed in 

the other parameters but were not conclusive as stand-alone 

maps, likely due to overall low concentrations (figs. 11 and 

13). Spatial turbidity data from September 16 also supported 

the evidence that the Balm Fork arm of the reservoir had 

higher algal productivity than other areas of the reservoir. 

Analyzing maps of multiple water-quality parameters provides 

a more complete understanding of spatial variation than any 

one parameter.

15.9

26.2

23.0

Base image from Esri, copyright, 2018. Coordinate reference system: NAD83 

UTM Zone 10N. Horizontal datum is North American Datum of 1983.

119°33'15" 119°33' 119°32'45" 119°32'30" 119°32'15" 119°32' 119°31'45" 119°31'30" 119°31'15"

45°

21'

45°

20'

45"

45°

20'

30"

45°

20'

15"

0 100 200 300 400 500 FEET

0 50 100 150 METERS

Total chlorophyll, in 

micrograms per liter

Chlorophyll-a discrete 

samples, in 

micrograms per liter

EXPLANATION

High: 4.9

Low: 0.1

15.9

Figure 11. A colorized map representing relative total chlorophyll concentrations throughout the reservoir at 1.5 feet deep on 

September 16, 2016, from 1150 and 1400 PDT. Data for the colorized map were derived from boat transects as shown in figure 3. Data 

were analyzed in ArcGIS using the Inverse Distance Weighted spatial analyst tool. Areas that were too shallow for the boat to sample 

were interpreted based on the nearest measurements. Discrete water samples were collected from the three noted locations as soon 

as the mapping was complete, and samples were analyzed in the USGS Oregon Water Science Center laboratory following EPA Method 

445.0 In Vitro Determination of Chlorophyll a. Mapping data were not corrected to laboratory results.
18 Temporal and Spatial Monitoring of Cyanobacterial Blooms at Willow Creek Reservoir, North-Central Oregon

tac18-1227_fig 12

119°33'15" 119°33' 119°32'45" 119°32'30" 119°32'15" 119°32' 119°31'45" 119°31'30" 119°31'15"

45°

21'

45°

20'

45"

45°

20'

30"

45°

20'

15"

0 100 200 300 400 500 FEET

0 50 100 150 METERS

Base image from Esri, copyright, 2018. Coordinate reference system: NAD83 

UTM Zone 10N. Horizontal datum is North American Datum of 1983.

Water temperature, in 

degrees Celsius

EXPLANATION

High: 21.99

Low: 18.15

Figure 12. A colorized map representing water temperature throughout the reservoir at 1.5 feet deep on September 16, 2016, from 

1150 to 1400 PDT. Data for the colorized map were derived from boat transects as shown in figure 3. Data were analyzed in ArcGIS 

using the Inverse Distance Weighted spatial analyst tool. Areas that were too shallow for the boat to sample were interpreted based 

on the nearest measurements.
Temporal and Spatial Monitoring of Cyanobacterial Blooms 19

tac18-1227_fig 13

119°33'15" 119°33' 119°32'45" 119°32'30" 119°32'15" 119°32' 119°31'45" 119°31'30" 119°31'15"

45°

21'

45°

20'

45"

45°

20'

30"

45°

20'

15"

0 100 200 300 400 500 FEET

0 50 100 150 METERS

Base image from Esri, copyright, 2018. Coordinate reference system: NAD83 

UTM Zone 10N. Horizontal datum is North American Datum of 1983.

Blue-green algae 

phycocyanin 

concentrations, in 

micrograms per liter

EXPLANATION

High: 5.1

Low: 0

Figure 13. A colorized map representing relative blue-green algae―phycocyanin concentrations throughout the reservoir at 1.5 feet 

deep on September 16, 2016, from 1150 and 1400 PDT. Data for the colorized map were derived from boat transects as shown in figure 3. 

Data were analyzed in ArcGIS using the Inverse Distance Weighted spatial analyst tool. Areas that were too shallow for the boat to 

sample were interpreted based on the nearest measurements.

Temporal and Spatial Monitoring of 

Cyanobacterial Blooms

Each monitoring method tested (camera, in-situ multiparameter instrument, spatial mapping) in 2015 and 2016 

at Willow Creek Reservoir was successfully used to collect 

valuable information. However, each method has benefits and 

limitations, and determining which equipment and method to 

use should be based on the resource managers’ goals and how 

the information will be used. Ultimately, the combination of 

all three methods helped provide details on timing, severity, 

spatial extent, and capacity for early warning that no single 

method would deliver. 

One objective of this study was to evaluate multiple 

monitoring devices, including the color surveillance camera 

and the multi-parameter water-quality instrument. The 

camera was deployed for approximately 8 months from 

2015 to 2016 and collected information about cyanobacterial 

surface bloom dynamics, including duration and frequency. 

Standard tools previously used to monitor blooms in the 

reservoir include analyzing routine samples (collected about 

once every 2 weeks) or viewing LandSat8 images (taken 

once every 16 days). With images of the reservoir captured 

every 15 minutes, the camera collected more thorough 

temporal coverage than the other data-collection methods 

could provide. The camera revealed that the presence of 

surface bloom scums or accumulations can change rapidly 
20 Temporal and Spatial Monitoring of Cyanobacterial Blooms at Willow Creek Reservoir, North-Central Oregon

(on the order of 15 minutes or less) due to a wind mixing 

effect, which could help inform routine toxin sampling and 

recreation. Other benefits of deploying a camera include the 

relatively inexpensive equipment costs and the ability to use 

the equipment for multiple seasons. Technology has improved 

since the Axis 214 camera (used in this study) went on the 

market, and using a modern color surveillance camera would 

provide higher color resolution and improve this collection 

technique. Limitations of monitoring with a camera in a 

remote location include the potentially poor cellular coverage 

for telemetry and the challenging logistics associated with 

positioning the camera above the water at the proper angle. 

While the camera could pan and capture images from multiple 

angles, the spatial coverage of the camera was limited and 

multiple cameras may be required for larger reservoirs. In 

areas of poor cellular coverage, telemetry via an alternate 

cabled Internet connection may be needed. 

Once the telemetry was established, the camera provided 

near real-time color images of the surface of the remote 

reservoir via a website interface to resource managers who 

were located about 200 mi away (fig. 9). Images may provide 

more useful information to the public than other types of data 

because images require minimal interpretation. Telemetered 

images could be made available to the public to inform their 

decisions about fishing and safe recreation (figs. 14–17). 

Additionally, telemetered images could be used as an early 

warning system that could prompt resource managers to 

collect samples for toxin analysis and to potentially issue 

recreational closures. In the future, the camera method could 

be adapted to utilize pigment-detecting software to automate 

the process and alert resource managers when a pigment 

concentration threshold is exceeded.

Figure 14. An algal surface accumulation occurring in the northwestern corner of Willow Creek Reservoir, north-central, Oregon, 

November 7, 2016, at 1223 PST. Photograph by U.S. Geological Survey.
Temporal and Spatial Monitoring of Cyanobacterial Blooms 21

tac18-1227_fig 15

Figure 15. An algal bloom occurring along the dam face in Willow Creek Reservoir, north-central Oregon, September 26, 2016, at 

1150 PDT. Photograph by U.S. Geological Survey.

Another objective of the study was to monitor the effects 

of cyanobacterial blooms on the reservoir’s water quality. 

During the 4 months that the continuous instrument was 

deployed in Willow Creek Reservoir, 17.5 percent of the 

values exceeded the Total Maximum Daily Load (TMDL) 

maximum limit of 9.0 standard units (Oregon Department 

of Environmental Quality, 2017), and the pH reached 

a maximum of 9.5 standard units. Those pH values are 

biologically relevant because such basic pH values can cause 

ammonia in the water column to remain in its un-ionized form, 

which can negatively affect fish gills and ultimately cause 

ammonia toxicity if concentrations are high enough (U.S. 

Environmental Protection Agency, 2013). The water-quality 

instrument data also revealed supportive trends among total 

chlorophyll, turbidity, and BGA-PC, and more information can 

be gleaned from these datasets. For example, with additional 

data and the development of a model, turbidity might become 

a suitable surrogate for total phosphorus concentrations in the 

reservoir. Stone and others (2013) developed a model using 

dissolved oxygen, specific conductance, and fluorescence data 

to obtain estimates of dissolved phosphorus concentrations 

in a reservoir in Kansas. These types of models may allow 

the inference of continuous nutrient concentrations that could 

help elucidate nutrient loading patterns and ultimately assist in 

controlling algal blooms. 

Continuous water-quality monitoring is often viewed as 

an expensive form of data collection because the instruments 

require ongoing maintenance and the data require auditing 

or adjusting (based on calibration and fouling corrections) 

to ensure their accuracy; however, numerous benefits can be 

derived from collecting multiple years of continuous data from 

an impaired water body. Continuous monitoring collects data 

during short-term events, when manual on-site sampling may 

not be possible, and helps define baseline conditions. Studying 

the baseline conditions will provide possible benchmarks, or 

goals, for restoration practices in the future. The continuous 
22 Temporal and Spatial Monitoring of Cyanobacterial Blooms at Willow Creek Reservoir, North-Central Oregon

tac18-1227_fig 16

Figure 16. An algal surface accumulation occurring in the northwestern corner of Willow Creek Reservoir, north-central Oregon, 

September 28, 2016, at 1048 PDT. Photograph by U.S. Geological Survey.

water-quality data were collected in 2015, which was a 

notably drier- and warmer-than-normal summer in Oregon 

(National Oceanic and Atmospheric Administration, 2015a, 

2015b, 2015c). Multiple years of continuous water-quality 

monitoring will reduce the effects of outlier years. Continuous 

water-quality data also provide information regarding the 

magnitude, duration, and frequency of the impaired water 

conditions, which could be useful when determining if any 

TMDL regulations are exceeded. It is important to note that 

the instrument measurements were taken from only one point 

and one depth in the reservoir. These values may not represent 

the conditions in other parts of the reservoir and extrapolation 

is unlikely to provide accurate information, as shown by 

Foster and others (2017).

The continuous water-quality data show that two distinct 

bloom events occurred during 2015, in May and August/

September. During both events, the magnitude of maximum 

physicochemical values and their diurnal variability were 

higher compared to non-bloom periods (fig. 6). Water-quality 

parameters measured in July (between bloom events) are 

suitable reference conditions, and were generally low (total 

chlorophyll: ≤ 10 μg/L; BGA: ˂ 1 μg/L; DO: ≤ 9.5 mg/L; 

pH: ≤ 9.0 standard units) with a minimal 10-day mean diurnal 

variation (total chlorophyll: 4 μg/L; BGA-PC: 0.4 μg/L; 

DO: 0.4 mg/L; pH: 0.03 standard units). The May bloom 

event was characterized by a maximum chlorophyll and 

BGA-PC concentration of 39.6 and 15.2 μg/L, respectively. 
Temporal and Spatial Monitoring of Cyanobacterial Blooms 23

tac18-1227_fig 17

Figure 17. A boat paddles through an algal bloom occurring in the northwestern corner of Willow Creek Reservoir, north-central 

Oregon, October 10, 2016, at 1109 PDT. Photograph by U.S. Geological Survey.

The dissolved oxygen and pH were relatively elevated (DO 

maximum= 12.3 mg/L; pH maximum= 9.1 standard units) 

and dissolved oxygen 10-day mean diurnal variability was 

twice as high as reference conditions in July. Chlorophyll 

and BGA-PC concentrations during the August/September 

bloom event reached 115.0 and 20.8 μg/L, respectively. The 

dissolved oxygen and pH values and trends appeared to have 

been tightly coupled with the algal biomass production during 

the August/September bloom; the dissolved oxygen reached 

18.5 mg/L and diurnal variability was 7.5 times higher than 

the reference conditions in July. A greater response of the 

water-quality parameters occurred for the August/September 

bloom than for the May bloom. One potential explanation 

for the more pronounced water-quality effects during the 

August/September bloom is that water temperature was 

warmer than in May and may have created more favorable 

conditions. Secondly, laboratory identification determined 

that the phytoplankton communities differed between the May 

and August/September blooms. Although Dolichospermum 

was a dominant genus in both blooms, Aphanizomenon was 

also considered dominant in the August/September bloom, 

indicating that Aphanizomenon may have a stronger influence 

on water quality. Increased variability of chlorophyll, 

BGA-PC, dissolved oxygen, and pH can indicate that 

ecosystem changes are occurring (Batt and others, 2013), and 

analyzing trend variability can be useful when monitoring and 

identifying blooms. 

Comparing the camera images to the trend of total 

chlorophyll concentrations (fig. 10) revealed that the two 

monitoring methods generally support each other. Chlorophyll 

concentrations were low (mostly < 25 μg/L) in May 2015, 

even though bloom conditions were occurring. A sample 

collected in the northwestern corner on May 9, 2015, and 

analyzed by Green Water Laboratories in Palatka, Florida, 
24 Temporal and Spatial Monitoring of Cyanobacterial Blooms at Willow Creek Reservoir, North-Central Oregon

revealed that microcystin concentrations were well below the 

State of Oregon’s guidelines for recreational water. The results 

of these monitoring methods illustrate one of the challenges of 

monitoring and managing harmful algal blooms. In this case, 

algal biomass was present, chlorophyll and other parameters 

increased in magnitude and variability, but the point sample 

indicated that the toxins at the moment of sampling were 

below harmful thresholds. Conditions and biomass can change 

quickly, and toxin concentrations may have varied during the 

weeks that the surface accumulation was visible. This example 

emphasizes the value of applying multiple monitoring 

approaches.

While the continuous water-quality instrument measured 

high frequency data from one location, the spatial mapping 

assessed the heterogeneity of the water chemistry throughout 

the reservoir in a discrete time period. Table 2 shows similar 

measured values from the stationary instrument and the 

mapping instrument, indicating that the mapping effort 

collected valid measurements that were not affected by 

movement. The spatial mapping was conducted continuously, 

without pausing to collect discrete samples, to minimize the 

effects of changing environmental conditions on the water 

chemistry. Considering that the boat returned to specified 

locations to collect discrete samples after the mapping 

was complete, the discrete chlorophyll-a results should 

be considered as approximate, or relative, values (fig. 11); 

mapping data were not corrected to laboratory results due 

to these limitations. EXO2 total chlorophyll probes provide 

relative values, emphasizing the importance of collecting and 

analyzing discrete samples. 

Spatially mapping the body of water may reveal areas 

to focus restoration efforts and areas with high BGA-PC 

concentrations to sample for toxins (Foster and others, 2017; 

Graham and others, 2017). A surface bloom is present in 

images from September 16, 2016, and the instrument data 

support that a bloom was occurring in the northwestern 

corner of the reservoir. The general patterns of water quality 

documented on that date showed that the Balm Fork arm of 

the reservoir was one area that contained high temperatures, 

super-saturated dissolved oxygen, and relatively high total 

chlorophyll readings. Based on the mapping route and time 

of day, the observed patterns in the data were not a result of 

sampling bias due to diurnal fluctuations. The spatial mapping 

data were collected around mid-day for each of the three 

events; however, the dissolved oxygen and pH often peaked 

later in the afternoon in the reservoir. Conducting spatial 

mapping events at specific times would collect more targeted 

data, potentially including the extremes for a given day.

Summary and Conclusions

This study displayed the effectiveness of monitoring with 

multiple devices concurrently. The camera images capture 

surface blooms, but do not collect information regarding 

changes or conditions in the water column. The waterquality instrument collects high-frequency data from the 

water-column, but determining when a bloom begins or ends 

requires trend interpretation. This continuous dual monitoring 

method showed when a surface bloom initiated and dissipated 

and revealed the magnitude, or potential severity, of the 

impacts to the water quality. Monitoring with multiple 

instruments provided a more comprehensive dataset than any 

one monitoring method. 

Identifying innovative and cost-effective monitoring 

approaches will become more essential as the frequency, 

duration, and intensity of cyanobacterial blooms increase, 

as predicted by Pearl and Huisman (2009). Currently, a 

lack of knowledge exists regarding the linkages between 

bloom occurrence and toxin production, and future research 

and monitoring that focuses on the relationships between 

water-quality parameters and toxin concentrations would 

improve the predictive and management value of such 

methods. Monitoring networks and spatial mapping could 

determine the extent, location, and frequency of affected areas 

during bloom events (Foster and others, 2017; Graham and 

others, 2017). Near real-time data may lead to abbreviated 

water-body closures, moderating economic damage due 

to loss of recreation and alleviating inconvenience to the 

public. Multiple years of data collection, along with local 

meteorological data, can be used to create predictive models 

for cyanobacterial blooms. Early warning systems and 

predictive models may be one way to minimize the risks of 

cyanobacterial blooms to recreational users of water bodies.

Acknowledgments

The author would like to thank staff at the U.S. Army 

Corps of Engineers for their support, access to Willow Creek 

Dam, and for helpful discussions, particularly Kathryn 

Tackley and Dan Turner. Fieldwork was successful due to the 

assistance of Dr. Frank Wilhelm and Sarah Burnet from the 

University of Idaho, as well as JoJo Mangano, David Piatt, 

and David Weathers from USGS. Mentorship and support 

were provided by Joe Rinella, Stewart Rounds, and Zach 

Freed of USGS. 
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Publishing support provided by the U.S. Geological Survey

Science Publishing Network, Tacoma Publishing Service Center

For more information concerning the research in this report, contact the

Director, Oregon Water Science Center

U.S. Geological Survey

2130 SW 5th Avenue

Portland, Oregon, 97201

https://www.usgs.gov/centers/or-water
Smith—Temporal and Spatial Monitoring of Cyanobacterial Blooms at Willow Creek Reservoir, North-Central Oregon—Scientific Investigations Report 2018-5083

ISSN 2328-0328(online)

https://doi.org/10.3133/sir20185083