U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2008–3009

March 2008 Printed on recycled paper

The risks C-HABs pose to source water and public health 

prompted the U.S. Environmental Protection Agency (USEPA) 

to add freshwater algal toxins from Cyanobacteria (cyano-toxins) 

to the USEPA drinking-water contaminant candidate list in 1998 

(U.S. Environmental Protection Agency, 1998). The World Health 

Organization also set a drinking-water guideline for the cyano-toxin 

microcystin-LR of 1 microgram per liter (Chorus and Bartram, 1999; 

World Health Organization, 2006). In addition to cyano-toxins, 

Cyanobacteria also are a source of the taste and odor compounds 

geosmin and methyl-isoborneol (MIB) (Chorus and Bartram, 1999). 

Together, these compounds and cyano-toxins have the potential to 

degrade source-water quality and impair public water-supply uses of 

surface water.

Cyanobacteria Monitoring Capabilities

The U.S. Geological Survey (USGS), with cooperators, has 

developed capabilities to study cyanobacterial blooms and their 

associated toxins as well as taste and odor compounds (fig. 2). Some of 

these capabilities follow:

Reservoir Monitoring

Regional reservoir surveys are done to evaluate the distribution 

and abundance of bloom-forming algae and allow for the tracking 

of algal blooms to estimate their persistence and spatial extent. 

Additionally, sampling for nutrients and other constituents of interest 

are done to evaluate correlations between water quality and C-HABs.

Continuous Monitoring

Multiple-depth water-quality monitors track physical and 

chemical properties that might be associated with algal blooms 

over multiple time scales. Experimental in vivo fluorescence 

(IVF) chlorophyll probes are used for tracking algal biomass and 

Cyanobacteria occurrence. In Texas, research is being done in 

cooperation with the U.S Army Corps of Engineers, the City of 

Houston, and the City of Waco to evaluate the ability of continuous 

data to predict the concentration of chlorophyll, Cyanobacteria, MIB, 

and other HAB-related compounds in surface water. This type of 

information is delivered by the USGS National Water Information 

System (NWISWeb) (U.S. Geological Survey, 2008) for continuous 

monitoring of algal bloom dynamics.

Ecological Data Collection

Limiting nutrient algal growth-rate bioassays are done to assess 

bloom regulation and nutrient limitation. Results from phytoplankton 

analysis yield algal biomass estimates and algal species composition to 

document algal bloom characteristics.

Investigation of Biological Constituents of Concern

Cyano-toxins and taste and odor compounds analyzed at the 

USGS Organic Chemistry Research Laboratory in Lawrence, Kan., 

are used to track reservoir source-water quality and evaluate linkages 

between environmental conditions and C-HAB occurrence.

Harmful Algal Blooms 

Harmful algal blooms (HAB) can occur when certain types of microscopic 

algae grow quickly in water, forming visible patches (for example, fig. 1) 

that might harm the health of the environment, plants, or animals (Centers 

for Disease Control and Prevention, 2004). In freshwater, species of 

Cyanobacteria (also known as bluegreen algae) are the dominant group 

of harmful, bloom-forming algae (Sinclair, Hall, and others, 2007). When 

Cyanobacteria form a harmful algal bloom (C-HAB), potential impairments 

include restricted recreational activities because of algal scums or algal 

mats, potential loss of public water supply because of taste and odor 

compounds (for example, geosmin), and the production of toxins (for 

example, microcystin) in amounts capable of threatening human health and 

wildlife (Centers for Disease Control and Prevention, 2004; Graham, 2006). 

Figure 1.  Surface algal bloom of Cyanobacteria (Anabaenopsis 

circularis) on Waco Lake, Texas, March 2005.

Monitoring Indicators of Harmful Cyanobacteria in Texas

Figure 2.  Reservoirs sampled for indicators of harmful

Cyanobacteria in Texas, 2006.

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EXPLANATION

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Monitoring Activities

In cooperation with the Texas Commission on Environmental 

Quality, 36 sites at 30 reservoirs (six reservoirs had two sites each) 

across Texas were each sampled once during 2006 as part of a study 

to assess the linkage between Cyanobacteria abundance and C-HAB 

indicators including microcystin, geosmin, and MIB (fig. 2). A subset 

of the six reservoirs with two sites each also were sampled at various 

times during 2006 to evaluate the seasonal nature of these linkages. 

Data collected during the study were entered into a geodatabase for 

spatial analysis. The geodatabase framework allows for spatial analyses 

of field data, laboratory results, and environmental data by relating 

site locations to data tables (fig. 3). A geodatabase query linking the 

site, sample, and tables of laboratory results was done to determine the 

number of detections recorded at source-water reservoirs. The outcome 

of the query is expressed as a map with graduated symbols representing 

the number of detections for the one-time reservoir survey sites and for 

the seasonal reservoir survey sites.

Over the years, monitoring of algal populations using traditional 

methods has identified a number of Texas reservoirs with potentially 

harmful Cyanobacteria. Since 2006, real-time, in-lake chlorophyllfluorescence monitoring using an IVF sensor has provided valuable 

information for tracking algal bloom formation. Inferred chlorophyll 

concentrations from the IVF sensor have been used to identify 

potential algal blooms and to track temporal patterns in algal biomass 

distribution. For example, continuous real-time data collected during 

2006 at Whitney Lake and at Waco Lake identified periods when 

potential algal blooms were developing. In the case of Whitney 

Lake, peaks in inferred chlorophyll concentration (fig. 4) were 

used to indicate when to begin water-quality monitoring, which 

involved integrating traditional sampling methods with modern 

sensor technology. Current (2008) real-time data from Waco Lake are 

available on the USGS NWISWeb at http://waterdata.usgs.gov/tx/nwis/

uv/?site_no=313430097113801

References

Centers for Disease Control and Prevention, 2004, Harmful algal blooms: 

Department of Health and Human Services, Centers for Disease Control 

and Prevention [fact sheet], accessed January 22, 2008, at http://www.

cdc.gov/hab/pdfs/factsheet.pdf

Chorus, Ingrid, and Bartram, Jamie, eds., 1999, Toxic Cyanobacteria in 

water: New York, E&FN Spon, 416 p.

Graham, J.L., 2006, Harmful algal blooms: U.S. Geological Survey Fact 

Sheet 2006–3147, 2 p. 

Sinclair, J.L., Hall, S.H., and others, 2007, Chapter 3—Occurrence of 

cyanobacterial harmful algal blooms workgroup report, in Hudnell, 

H.K., ed., International Symposium on Cyanobacterial Harmful Algal 

Blooms (ISOC-HAB), Research Triangle Park, N.C., 2005, Proceedings: accessed January 22, 2008, at http://www.epa.gov/cyano_habs_

symposium/monograph.html 

U.S. Environmental Protection Agency, 1998, Announcement of the drinking water contaminant candidate list: Federal Register, v. 63, no. 40, 

p. 10,273–10,287.

U.S. Geological Survey, 2008, National Water Information System 

(NWISWeb) data available on the World Wide Web at http://waterdata.

usgs.gov/nwis 

World Health Organization, 2006, Guidelines for drinking-water quality, 

third edition, incorporating first addendum—Volume 1. Recommendations: Water Sanitation and Health, accessed January 22, 2008, at 

http://www.who.int/water_sanitation_health/dwq/gdwq3rev/en

—Richard L. Kiesling, Robin H. Gary, and Marcus O. Gary

_________________________________________________________

Any use of trade, product, or firm names is for descriptive purposes 

only and does not imply endorsement by the U.S. Government.

_________________________________________________________

For additional information, contact 

Director

USGS Texas Water Science Center

World Wide Web: http://tx.usgs.gov/ 

E-mail: gs-w-txpublic-info@usgs.gov 

San Antonio

Austin

Houston

Dallas

Fort Worth

Abilene

Wichita Falls

Waco San Angelo

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North America Lambert Conformal Conic projection

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LOCATION MAP

TEXAS

EXPLANATION

Seasonal reservoir survey 

site—Number of detections

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!( 5–6

One-time reservoir survey 

site—Number of detections

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Study area

Figure 3.  Number of detections of geosmin, methyl-isoborneol,

and microcystin at the 36 reservoir sites sampled during 2006.

Figure 4.  Chlorophyll concentrations at Whitney Lake, Texas,

inferred from in vivo fluorescence (IVF) measured by an inlake, real-time IVF sensor. Peaks show a pattern of increasing

chlorophyll concentrations associated with a developing algal

bloom during June 20–23.

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INFERRED CONCENTRATION,

IN MICROGRAMS PER LITER

JUNE 2006