Algal Blooms in Lakes
brochure has been produced to answer the more frequent enquiries
received by the Ministry of Environment, Lands and Parks
(now called Ministry of Water, Land and Air Protection) on
blue-green algal blooms in lakes and to provide you with
general information on related water management concerns.
Are Blue-Green Algae?
algae are not true algae, but are more properly photosynthetic
bacteria and can also be called cyanobacteria. They
are commonly found in lakes, ponds and wetlands. They
usually occur in small numbers and are invisible to
the casual observer.
What Are Blooms?
conditions are favourable (most often during hot, calm
weather), algae increase dramatically and they become
easy to see. This condition is generally called a bloom.
algal blooms occur, huge numbers of algae accumulate on the
surface of lakes and ponds resembling thick pea soup and are
often blue-green in colour. Although blooms occur naturally,
water bodies which have been enriched with plant nutrients
from municipal, industrial and agricultural sources are particularly
Why are Blooms Important?
unsightly; and blue-green algal blooms may be toxic if ingested
by wildlife, livestock or humans.
How are Blue-Green Algal Blooms Toxic?
two types of toxins produced by strains of blue-green algae:
- Neurotoxins affect the
nervous and respiratory systems and can cause muscle tremors,
stupor, staggering, rapid paralysis, respiratory failure and — often
within 30 minutes — death. Most frequently, animals are
found dead close to the lake or pond.
- Hepato-toxins affect
the liver and cause a slow death, up to 36 hours or longer
after drinking water contaminated with toxic strains
of blue-green algae. The animals appear ill, may show jaundice
(yellowing of the mucous membranes or the white of the
eye), photo-sensitization (swelling and fluid under the skin,
may peel, especially in the unpigmented areas), or severe
What are the Effects on Animals?
or other domestic animals have no other source of drinking
water, they may be poisoned by drinking water contaminated
with toxic strains of blue-green algae. The most common occurrences
of blue-green algal poisoning concern cattle.
Every year some cattle deaths are associated with blue-green
algal blooms, particularly in the interior of British Columbia.
Wind may concentrate the algae on the shoreline to increase
the concentration of the poison in that area. Older stock
may be able to wade into the lake beyond the bloom to drink
and are not affected, whereas young stock are forced to drink
closer to shore and may be poisoned.
What are the Effects on People?
as susceptible as animals to the toxic effects of certain strains
of blue-green algae in untreated drinking water.
Water during a bloom is both objectionable in appearance and
odour. It is unlikely that older children or adults will
drink it voluntarily. However, younger children may be less
After ingesting water containing toxic blue-green algae, symptoms
such as fever, dizziness, stomach cramps, vomiting or sore
throat may persist for several days.
How can We Prevent Poisoning from Blue-Green Algal Blooms?
algal blooms are more toxic than others and therefore all blooms
should be treated with caution.
One of the first signs of toxin contamination in a water body
is the presence of distressed and dead wildlife, waterfowl
or livestock along the shoreline.
If you observe dead or distressed animals along a shoreline where
a bloom is obvious, immediately contact the nearest Regional
Health office or the nearest BC Ministry of Water, Land and
Air Protection regional office.
If livestock is affected, also contact a veterinarian or the
nearest office of the BC Ministry of Agriculture, Food and
Water suspected of being contaminated with toxic strains of blue-green
algae can be sampled and tested for toxicity.
Do not drink
untreated water from water bodies regardless of whether noticeable
blooms are present. In addition to possible
health risks from algal blooms, there are other gastrointestinal
illnesses which can also be contracted by drinking untreated
water, including Giardiasis or Beaver
Key Points to Remember...
- Do not wade or
swim in water containing visible blooms.
- If blooms are present, do not allow livestock or pets access
to the affected water. Alternative sources of drinking water
for livestock and pets should be provided.
- Blooms intensify in non-moving or stagnant water. If possible,
natural blockages in creeks flowing into or out of the water
body should be removed to encourage the free flow of water.
- Divert surface runoff from livestock feedlots away from streams
and lakes. Blooms flourish from runoff flowing through animal
If a Bloom is Detected, How Long Will it Last?
most blooms are short-lived and an affected area will likely
be safe again in a number of days or within a one to two week
period. If unsure, contact your local health office, or the
nearest Ministry of Water, Land and Air Protection office.
If your concerns are related to livestock, contact the nearest
office of the BC Ministry of Agriculture, Food and Fisheries.
Government office telephone numbers are listed in the blue
pages of your telephone directory.
published in August 1998
August 3, 2001