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Report to the Legislature:

At the request of Representative Keffer, potential research and management strategies for toxic golden algal blooms are presented. Toxic golden algae have killed millions of fish since 1985. If successful, these proposed research and management options will protect the economic and ecological values of our watersheds.


  • Brazos River Authority
  • Tarleton State University
  • Texas A&M University
  • Texas Agricultural Experiment Station
  • Texas Department of Health
  • Texas Parks and Wildlife Department
  • University of Texas
  • U.S. Geological Survey

Report to the Legislature

Summary | Overview | Work Areas | Appendices

Toxic Golden Algae in Texas: An Overview


Toxic golden algal blooms have killed over 12 million fish in Texas since 1985, resulting in the loss of millions of dollars worth of dead fish, lost revenue to local economies, and lost time and resources involved in responses to the fish kills. Blooms are projected to continue and to expand into other river basins in Texas. At the request of Representative Keffer, the Harmful Algal Bloom Workgroup created this report to detail potential actions needed to understand how golden algal populations grow and become toxic, and how they can be managed in our lakes, rivers, and fish culture facilities. Problems caused by golden algae are not likely to be easily or quickly solved. Controls, particularly in lakes and rivers, may involve large-scale changes in nutrients and salt concentrations in the impacted watersheds.


The golden alga is a microscopic, free-floating, yellow-green algae. Algae are plants that are usually aquatic and lack true stems, roots, and leaves. The golden alga, whose scientific name is Prymnesium parvum (“perm-knee-z-um parvum”), lives in brackish water. Large concentrations of the golden alga (an algal bloom) color the water yellow to coppery-brown and may release the toxin prymnesin. Little is known about the cause of the blooms and toxin production. The toxin disrupts the functioning of the gills in fish and clams, killing them after extended exposure. Previous toxic blooms in Texas have killed hundreds of thousands of fish at a time, although aquatic insects, birds and mammals have not been impacted. The Texas Department of Health has stated that the golden alga is not known to harm humans; however, people should not collect dead or dying fish to eat.

Historical Exposure:

This toxic alga has killed fish on five continents. Evidence suggests that the golden alga probably caused fish kills in Texas as early as the 1960s, but it was first confirmed in Texas during a 1985 fish kill on the Pecos River. Since 1985 the range and impact of this organism has increased to include portions of the Brazos River, the Colorado River, and the Red River basins.

Recent Events:

During the winter and spring of 2001, significant fish kills caused by the golden alga occurred on three Brazos River lakes (Possum Kingdom Reservoir, Lake Granbury, and Lake Whitney) and on one lake in the Red River basin (Diversion Lake). Texas Parks and Wildlife Department’s (TPW) Dundee Fish Hatchery, which uses water from Diversion Lake, experienced a total loss of fish production due to the golden alga twice during 2001. In October 2001, golden algal fish kills occurred in E.V. Spence Reservoir on the upper Colorado River and in Moss Creek City Lake near Big Springs. The U.S. Geological Survey has identified golden algae-like cells in four additional lakes in Texas (Bardwell, Navarro Mills, Grapevine, and Cooper), although fish kills from toxic golden algal blooms have not been reported in these areas.


Several methods to control the golden alga and its toxin have been tried in fish culture ponds with mixed success. Fish culture treatments may pose threats to sportfish and other organisms if used in public waters. Available treatments do not offer effective or feasible methods for the control and management of golden algal blooms in Texas waters.

Ecological Impacts:

More than twelve million fish have been killed by toxic golden algal blooms in Texas since April 1985; over 7.6 million fish were killed in lakes and rivers, and 5.1 million fish were killed at the Dundee Fish Hatchery during the 2001 production season. Many economically important fish have been affected, including largemouth bass, smallmouth bass, striped bass, catfish, crappie, and rainbow trout. In 1986 on the Pecos River, approximately 200 blue suckers and 3,600 Rio Grande darters were killed; both of these fish are on the Texas list of threatened animals. Several other state or federally endangered or threatened fish occur in areas of previous golden algal fish kills, and future blooms may affect these protected animals. Despite killing large numbers of fish, golden algal blooms do not permanently poison the water. Although many fish were killed in Possum Kingdom Reservoir in 2001, post kill monitoring showed shad reproducing well and large catfish still being caught. Few largemouth bass older than one year were found, however, indicating that the entire recovery process may take years.

Economic Impacts:

According to an August 2001 article in a Possum Kingdom area newspaper, the Possum Kingdom Chamber of Commerce predicted four year losses of $18 to $20 million for the area’s economy. These losses result from cancelled travel plans, lost bait and tackle sales, and reduced demand for fishing guides. In 2001 the number of fishing guides dropped by more than half.

The value of the fish losses in Texas since 1985 is nearly $4.5 million in current dollars. At the Dundee Fish Hatchery, the loss in 2001 was approximately $680,000. ($426,000 was the value of dead fish, and $254,000 was the cost to acquire and transport new stock from other states.) Other economic impacts which are difficult to measure include costs associated with the investigation of fish kills, the restocking of lakes, decreased attendance in state parks, and decreased revenue from fishing license sales.


The public demanded action to control the golden alga. This demand led to a public meeting in the Possum Kingdom area in the summer of 2001. As a result of this meeting, TPW began coordinating the effort to address golden algal threats in Texas. The effort continues under the legislatively-established Toxic Substances Coordinating Committee’s Harmful Algal Bloom Workgroup comprised of representatives from several state agencies and universities. This report, prepared by the Harmful Algal Bloom Workgroup, outlines potential research and management options for the golden alga in Texas waters. Although TPW coordinated this report, the majority of work described would be performed by other agencies and universities. TPW neither has the funds or resources necessary to accomplish these tasks. TPW is interested in performing the fish culture management work but cannot support it within its current budget.

Potential Work:

Potential work in five areas is needed to achieve the goal of managing impacts of the golden alga in Texas. The work focuses on golden algal problems in lakes and rivers and in fish culture facilities, which require different management approaches. Each element of work completes a different piece of the puzzle and is needed to understand how golden algal populations grow and become toxic, and how their impacts can be managed. Although some of the work can occur simultaneously, some of the goals described are dependent on the success of other goals. The five areas of work are summarized below with estimated costs, although operational costs and budget numbers are likely to change over time. Specific budgets for each major area of work are available upon request.

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Additional Resources :

Download the 23-page Report to the Legislature media download(PDF 723.1 KB).

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