|What is golden alga and how does it kill
The golden alga, Prymnesium parvum, is a tiny,
one-celled aquatic organism about the size
of a human blood cell. The alga is motile with
two “tails” called flagella that
help it to move through the water in lakes
and ponds. A single drop of lake water may
contain well over 2,000 cells of golden alga.
Biologists suspect that golden alga is relatively
new to Arizona and they consider it a nuisance
Golden alga releases unique toxins that
affect gill-breathing aquatic organisms (mainly
fish and clams). The alga is a rapid growing
and resilient algae species, out-competing
other algae for nutrients and thriving in
a wide variety of environmental conditions.
In a bloom situation (a bloom is an explosive
increase in the population of one or several
species of algae), enough toxins are released
into the water to kill fish and other gill
breathers that come in contact with it. The
toxins cause fish gills to bleed internally,
and lose their ability to exchange water
and absorb oxygen. Fish then die of asphyxiation
(lack of oxygen).
Golden alga toxins have no apparent lethal
or harmful effects on animals that do not
breathe through gills. The impacts to fish
populations vary and are most often temporary.
Algae blooms may last for days or weeks.
Blooms may occur a couple times a year, or
not at all in some years. The environmental
conditions that support golden alga are broad,
and little is known about the specific and
complex conditions that allow it to gain
a competitive edge over other species, or
about what causes a "bloom" that
results in fish kills.
According to reports from other states and
recent trends in Arizona, the majority of
golden alga fish kills occur during the winter
and spring months when water temperatures
range from 55-80 degrees Fahrenheit. Winter
conditions are not favorable for other, common
kinds of beneficial algae normally found
in our inland waters, which likely gives
the golden alga a competitive edge.
Generally speaking, golden alga also prefers
more saline waters, which may also help a
bloom get started. Although factors such
as water temperature and salinity are somewhat
helpful in predicting lake conditions suitable
for golden alga, there are also many documented
exceptions in Arizona and other states.
Is it harmful to humans, pets or other animals?
Golden alga blooms are not a public health threat. The golden alga produces
a unique toxin that damages gill functions and causes fish to suffocate because
they can’t obtain oxygen from the water. The algal toxins are only
harmful to gill-breathing organisms such as fish and clams.
Arizona Department of Health Service officials
have stated that human health is not affected
by exposure to golden alga or their toxins.
Studies indicate the toxins are not passed
through the food chain or absorbed into the
flesh of fish. Consequently, healthy fish
caught from infested waters are safe to eat.
Still, people should exercise common sense:
do not pick up or eat dead or dying fish.
Cattle and other animals have been observed
drinking from rivers during ongoing golden
alga fish kills in Texas with no apparent
adverse effects. The bottom line: golden
alga blooms are harmful to animals (fish
and clams) with gills, but the alga and their
toxins don’t harm animals or people.
Where does it occur?
Golden alga was first identified in Arizona
in April 2005. To date, golden alga has
been confirmed in various public and private
waters in the greater Phoenix area and
in three reservoirs on the Tonto National
Four Urban Fishing Program waters have been
infested: Water Ranch Lake (Gilbert), and
Alvord Lake at Cesar Chavez Park, Cortez
Lake and Desert West Lake in Phoenix. It
has been found in Saguaro Lake, Canyon Lake
and Apache Lake.
Golden alga was first discovered in the
United States in Texas in 1985. Since then,
it has caused fish kills in five major river
systems and over 25 lakes or reservoirs in
Texas. Texas officials have estimated the
direct economic loss of over 18 million fish
due to golden alga as $7 million. This toxin
producing algae has now been documented from
12 states ranging from North Carolina to
Georgia to Wyoming to Arizona.
How can it spread?
Nobody knows with certainty how golden alga
is spread from one body of water to another
or how it was spread into Arizona. It may
travel along river or canal pathways, or
by businesses trucking products in water.
Water birds such as ducks, geese, herons
and cormorants, or humans transporting
water in live wells, bilge tanks, minnow
buckets or wet clothing or equipment, may
spread golden alga. Also, the resting cyst
stage of golden alga can reside in dried
lake sediments and potentially be dispersed
by strong winds.
What are the signs of a golden alga bloom?
Water Appearance: When
golden alga becomes more abundant during
a bloom cycle in a lake, the water begins
to turn yellowish, yellowish-copper or a
brownish, tea color. Another sign is foaming
at the surface of the water in areas where
there is a lot of wave action or water is
agitated or stirred up. However, these conditions
can also come from other sources, and do
not always indicate a golden alga bloom.
Additionally, golden alga has proven to be
toxic in waters where these visual conditions
have not been readily apparent.
Dying or affected fish: Fish
exposed to golden alga toxins may swim slowly
or erratically just below the surface, lie
listlessly along the bottom in shallow areas,
or show no normal avoidance to human disturbance
The toxin affects gill-breathing fish and
clams by disrupting the uptake of oxygen
across the gills. In the later stages, fish
will act as if there is no oxygen in the
water. Fish will seek areas with no toxicity
or lower toxicity. If clean water flows into
a lake, fish will often concentrate in these
Visible signs of exposure to the toxins
include redness or hemorrhaging at the base
of fins, around the mouth area, under the
chin, and along the belly of fish. After
prolonged exposure, there is blood loss from
broken capillaries (hemorrhaging) of the
gills, resulting in a pink or pale red appearance
to the gills.
Can fish escape a toxic golden alga bloom?
Yes, they can escape a localized bloom in
a lake if there is a nearby toxin-free
area. Early effects of the toxin are reversible
if the fish can swim to a toxin-free area
or an area of low toxicity.
In a larger reservoir or lake with a complex
shoreline and varied depths, all of the fish
may not be killed during a bloom, although
there may be individual coves where significant
mortality occurs as the fish become cut off
from the main part of the lake by the bloom.
In a small pond or lagoon, however, many
or all of the fish present may be killed
if a bloom is not promptly treated and is
allowed to spread across the entire water
What are the ecological and economic impacts?
It is too early to tell at this time what
the impacts may be in Arizona. Potentially,
the negative impacts may be significant
at a particular water, especially in larger
lakes and reservoirs. While golden alga
toxins can affect all species and sizes
of fish, most of the fish killed at Saguaro,
Canyon and Apache lakes have been a 2-6
inch forage fish, threadfin shad. These
fish grow quickly and lay many eggs for
rapid reproduction. Because of this, a
reservoir can recover, even from a massive
fish kill, if the waterbody has ample time
between fish kills. However, forage fish
do form the basis of the food chain and
on-going fish kills may harm larger game
fish in two ways, directly by toxicity
and indirectly by reduced food supply.
Most fish kills, however, do not continually
affect the entire lake and different parts
of the lake may continue to support excellent
Smaller, more intensely managed urban lakes
can be treated with chemical algaecides,
and fish can be replaced by restocking. To
maintain their fish populations and control
golden alga, lake owners must increase their
operating budgets to cover costs associated
with lake monitoring and testing, algaecide
treatments, and the purchase of replacement
Where else can I read about golden alga?
The Texas Parks and Wildlife Department provides
information on this problem to other agencies,
universities and the public. Their
Web site, offers helpful information
on golden alga and other harmful algal
There is limited scientific information
on basic ecology and distribution of golden
alga in inland waters of the United States.
So far, no one has found a practical way
to stop golden alga blooms and the fish kills
they cause. Biologists hope ongoing and future
research, monitoring, teamwork and collaboration
will eventually find efficient solutions.
Does golden alga occur throughout the water
Golden alga can occur throughout the water
column, depending on the water’s depth.
The cells need only moderate light for photosynthesis,
so they may be limited by how deep the sunlight
reaches. Generally, few golden alga are found
more than 20 feet below the lake surface.
However, some parts of the golden alga life
cycle can occur in the dark.
Resting cysts of golden alga (another stage
in the life cycle) sink to the bottom of
the water column after formation. This alga
is different from other algae. Not only can
it produce its own food from photosynthesis,
but by secreting its toxins it can also capture,
then eat and absorb other microscopic organisms,
primarily other species of planktonic algae
and bacteria, for sustenance.
Will warm water cause a golden alga bloom
Warmer waters may allow the algal community
to change, which can decrease a golden alga
bloom. However, if golden alga becomes numerous
in the phytoplankton (algal) community, it
can last all year despite rising temperatures.
Fish kills due to golden alga have occurred
in some Texas lakes and rivers throughout
the summer months. Worldwide scientific literature
states that golden alga is not toxic at 86
degrees Fahrenheit or above. Texas hatcheries
have seen decreases in golden alga numbers
and impacts during the heat of the Texas
Most of the documented golden alga blooms
and associated fish kills occur during seasons
when water temperatures are between 55-80
degrees Fahrenheit. Winter conditions are
not favorable for other, common kinds of
beneficial algae normally found in our inland
waters, which likely gives the golden alga
a competitive edge.
How do scientists measure the amount of
golden alga in the water?
Biologists collect water samples from various
lake locations and conduct cell counts to
estimate how many golden alga cells are in
the water. Powerful microscopes are necessary
to identify this one-celled organism. A small
amount of the water sample is put on a specialized
slide underneath a microscope and then golden
alga cells inside a grid are counted (each
cell is quite small).
Cell counts do not always correlate with
toxicity, although increased cell counts
were found prior to the fish kills in Texas.
Golden alga can produce enough toxin to cause
a fish kill when cell concentrations are
as low as 10,000 cells/milliliter, but fish
losses in Texas typically have not occurred
until algal density was at 20,000 cells/milliliter
How do we get the answers we need?
The Arizona Game and Fish Department is
working with experts from the Texas Parks
and Wildlife Department, Arizona Department
of Environmental Quality, Arizona Department
of Health Services, University of Arizona,
and lake management consultants to learn
more about golden alga, how to monitor
it, and how to identify feasible options
to address it where possible.
Texas Parks and Wildlife Department (TPWD)
has a Golden Alga Task Force that is working
with researchers, other agency officials,
and interested parties within and outside
Texas to research, monitor and control harmful
golden alga in Texas. In 2003, the Texas
Legislature authorized the use of $600,000
per year for two years for research on golden
alga in targeted areas. These areas include
the development of management tools, approaches
and technologies to help aquatic managers
detect, combat, and manage golden alga in
Texas. Another $450,000 was dedicated for
continued golden alga research in 2005.
TPWD is also working on several other projects
to better understand and control golden alga.
The solutions to the problems of toxic golden
alga (like other harmful algae species) will
not be solved easily or quickly, although
progress and successes will occur.
What is the Arizona Game and Fish Department
doing about golden alga?
The Arizona Game and Fish Department is working
diligently to learn more about this recently
discovered alga in Arizona, to inform the
public, to monitor affected lakes, to investigate
all fish kills, and to work collaboratively
with other affected stakeholders. There is
simply no "silver bullet" to eliminating
The Arizona Game and Fish Department has
implemented cooperative efforts that give
Arizona the best chance to mitigate the impacts
of these events and address the potential
for future outbreaks. The department is coordinating
efforts to monitor fish kills and also to
manage the recreational fisheries in these
waters with the lake authorities and managers,
state agencies, and other stakeholders. These
monitoring, management and research efforts
are significant and important.
The four lakes in the Salt River system
(Saguaro, Canyon, Apache, and Roosevelt)
are being monitored regularly for algal blooms
and fish kills. The department has set up
a contact number (623-236-7257) for the public
to report any observations of golden alga
blooms or fish kills. Fish kill and other
lake observation information suspected to
be connected with golden alga blooms may
also be emailed to the department at email@example.com.
The department is also working with city
officials to monitor, test and control the
golden alga at Urban Fishing Program lakes.
The city park departments have been responsive
in treating their affected lakes with algaecides.
After each treatment is completed, the department
tests the lake waters to determine if the
treatment was successful in killing off the
algae. When lake water quality is satisfactory,
fish stockings then resume. When necessary,
the lake will be restocked with sunfish,
bass and catfish. Public notices are posted
around the Urban Fishing Program lakes to
advise park users of current management and
fish stocking activities.
Note: Although ponds and lakes smaller than
a few hundred surface acres can be treated
successfully, these treatments may not be
economical or feasible in the larger and
more complex reservoirs and rivers.
Unfortunately, the golden alga situation
is analogous to red tides in coastal waters.
Red tides are caused by different toxic algae
that also result in widespread fish kills.
Extensive research has been conducted on
red tide algae in marine environments for
over 30 years that has increased knowledge
about the algae, but has not yet resulted
in viable treatments to control bloom outbreaks.
The ultimate goal of the department is to
learn enough about golden alga to be able
to effectively manage it and its impacts.
Until viable management options are determined
though, the department’s emphasis remains
on monitoring, management and outreach about
harmful golden alga blooms.
How can I help?
If you see dead or dying fish or large numbers
of fish behaving strangely, take note of
the species and sizes of fish affected,
approximate numbers of fish observed, and
the location(s) where fish were observed.
Report your observations as soon as possible
to the Arizona Game and Fish Department
at firstname.lastname@example.org or
call (623) 236-7257. Common sense should
be exercised by not picking up dead or
dying fish for consumption.
To prevent transporting the alga to other
- Drain all lake water from watercraft,
live wells and equipment before leaving
- Rinse out watercraft, live wells and
fishing equipment at home and allow
it to dry before
using it at another lake or river.
- Do not move water, aquatic wildlife
or plants (fish, frogs, tadpoles,
aquatic weeds, etc.) offsite.
How can I learn about the most up-to-date
Visit the Department Web site at www.azgfd.gov for
current information on golden alga and harmful
algae blooms in Arizona. You can also sign
up to receive, via e-mail, information directly
from the department at www.azgfd.gov/signup.
For more information on protecting our waters
go to: www.protectyourwaters.net.
Alga or Algae?
The term “alga” is used when only one species is being referenced,
such as Prymnesium parvum, the golden alga. If the discussion is about several
species (or a group of species), then the term algae is used.