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Natural Resources Extension Program
Toxic Algae: Potential in Drought Limited Water Supplies
By Gene Surber, Natural Resources
Specialist, MSU Extension Service
"Of
greatest concern is that which is toxic to livestock."
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The dry conditions throughout much of Montana may be
ideal for algae growth to appear on the limited stock
water supplies. Algae growth usually occurs in late
summer during the hottest times of year. Of greatest
concern is that which is toxic to livestock.
There are many groups of algae in Montana, but only
three members have species that produce lethal poisons
to livestock. Only three poisonous microscopic species
of the blue-green algae group are found throughout Montana
(only one documented in Montana) and our neighboring
states and provinces.
The most common visible signs will be water that is
dark-green to blue-green and may even be greenish-brown
to red, hence the name Blue-Green Algae. In order for
these algae to bloom the right conditions of temperature,
nutrients and light must be present. Lower water levels
in ponds and reservoirs allow light to penetrate closer
to the bottom of the water thereby providing the sunlight
for photosynthesis necessary for growth. During dry
conditions when the water levels are low there is bare
soil around and above the water, which provides a solar
collection area that increases soil temperature, which
in turn increases the temperature of the water in the
pond or reservoir. Water temperature around 72-80 degrees
F for several days are adequate to stimulate growth.
The low level of water increases the concentration of
nutrients in these water sources, which also combines
to provide the nutrients necessary for the algae to
grow.
Toxic Blue-Green Algae blooms are toxic to all warm-blooded
animals, including humans. Fish kills associated with
Blue-Green Algae blooms are most likely from the depletion
of oxygen in the water and not as a result of the toxin
produced. The Montana Department of Environmental Quality
indicated that fish taken from waters infested with
toxic algae are not likely to cause secondary poisons
if eaten in moderation, they may taste “weedy.”
There is no known antidote to be affective at counteracting
the effects of the toxin once it has been ingested.
There are two types of toxins produced. A peptide type,
which causes liver damage, but is rarely fatal. Symptoms
are diarrhea, nausea, cramps or general lethargic and
unthrifty animals. The other type is an alkaloid, which
causes death in a relatively short time. Early symptoms
from the alkaloid include staggering, muscle spasms,
labored breathing and/or convulsions. Death is caused
from respiratory failure and a very rigid neck observed
at death.
Not all algae blooms are toxic. To determine if an
algae bloom is of the toxic nature, look at several
items. Mats of algae floating on or below the surface
of the water, having a stringy texture that can be picked
up are probably a harmless green algae. All toxic or
potentially toxic blue-green algae present themselves
as surface scums. These algae scums are not stringy
or easily picked up. They are slippery, clotted masses
of cells that readily fall apart when attempting to
pick them up. Look for scum mats on the down wind side
of the pond or reservoir. Observe all animals, including
gophers, waterfowl, and others that rely on the water
for survival. If there is a toxic bloom any animals
making use of the water where the scum is present will
show the effects.
Suggested management alternatives:
The best way to prevent algae poisoning is to be aware
of the conditions that can produce the poisonous bloom
and to prevent animals from drinking the surface scum
when present. Producers should check all livestock watering
areas in hot, dry weather for light to heavy green coloration
of the water. If a surface scum is present, manage it
as if it were a toxic bloom.
Keep livestock, wildlife and pets away from the bloom
scum: use an alternate water source. If no other source
of water is available, the next best thing is to allow
animals to drink only on the upwind side of the reservoir
or pond where wind and water currents float the scums
away from the shoreline. It is also possible to construct
a floating barrier that sinks into at least the top
4 inches of water which will keep the surface scum away
from the area where animals drink. This type of barrier
can be built of logs, Styrofoam, or other floating materials.
It must isolate the drinking area completely and not
allow the surface scum to leak into the area. The barriers
should be large enough and over deep enough water so
animals will not be able to drink beyond it. Once scum
has formed it is not practical to build an effective
barrier to clear the scum away. If conditions are likely
to favor a bloom, it is best to build the barrier before
the scum develops.
Another option is to pump water via a waterline from
a subsurface location in a deeper part of the reservoir
to a water tank. Transferring the water to the tank
can be done by one of several methods, gravity, solar,
wind, electric or motorized pumps.
Chemical control with herbicides is an option and can
be directly applied to lakes and ponds to control most
algae growths of the colonial, filamentous, and single
cell types. However, some are highly toxic to aquatic
animals and should be avoided or used with extreme caution
and use may require a special license. There are two
basic herbicides used in ponds and lakes to control
algaes, copper sulfate products, and diquat.
Chelated copper complexes and copper sulfate (Bluestone)
are the most effective at controlling algae. However,
copper is a toxic metal that is long-lived (persistent)
in the environment. Copper sulfate can be toxic to fish
and aquatic animals at concentrations near levels used
to control algae, especially in soft water. Copper toxicity
increases as water hardness decreases. Copper sulfate
is not as safe to use as chelated copper compounds and
it should not be used in soft waters (alkalinity values
less than 50 mg/L, but most of Montana surface waters
are higher). No water-use restrictions are associated
with copper compounds.
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