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Blue-green algae are a common form of phytoplankton found in Lake Champlain. Most of the time, other forms of algae are more abundant than the blue-greens, so most people don’t notice them. Just like the plants in your garden, all algae in Lake Champlain need nitrogen and phosphorous. In the late summer, when nitrogen concentrations in the Lake can become low, the blue-green algae have an advantage because they can pull nitrogen from the air. All other algae need nitrogen in a dissolved form in the water. To extract nitrogen from the air, however, the blue-greens must be very near the surface.
During periods of calm weather, the blue-green algae can float at the surface (which is also the best location for photosynthesis), remove nitrogen from the air, and grow in abundance. We see this as a blue-green surface scum, or algae bloom. The scum is a mixture of the blue-green algae themselves, the mucus they secrete to stay at the surface and discourage small animals from eating them, and bubbles of air. When the wind begins to blow again, it breaks up the surface scums. Rains also carry more dissolved nitrogen to the Lake, creating opportunities for other algae to grow. With either wind or rain, blue-green algae fades into its background role.
Most of the time, the blue-green algae blooms that occur are not dangerous. They are certainly a nuisance for folks who want to swim or boat on the lake, but they will not harm you. Occasionally, this situation changes. For reasons not completely understood, some types of blue-green algae can begin producing toxins during blooms. Toxins are released as the cells of the algae become old, deteriorate and die. Not all blue-green algae produce toxins nor does the presence of the toxin-producer indicate that a toxin bloom is forming. Most of the time, both toxin-producing and non-toxic organisms occur within the same bloom. Toxin production also varies within a single season and from year to year. No one has yet discovered how to predict the occurrence of a toxic bloom.
Toxic blue-green algae blooms have been recorded around the world, from Finland to China. The first documented reports date back to the late 1800s in Australia. Fish, birds and mammals including sheep, horses, cattle and dogs have died after ingesting blue-green toxins. Although a few human deaths have been reported, blue-green algae toxins are generally not fatal to people. However, those who swim through a bloom and swallow significant amounts of water can sometimes develop skin rashes, gastrointestinal disorders and heart problems.
Blue-green algae give drinking water an "off" taste, whether toxin-producing species are present or not. Lakeshore residents with shallow drinking water intake pipes that might pump in blue-green algae should be cautious. No one should drink water from the Lake without treatment. While the taste of a non-toxic algae bloom is simply unpleasant, the health effects of long-term exposure to blue-green toxins are not known. Therefore, it is prudent to avoid ingesting any blue-green algae infested waters.
It is impossible to know when and where toxic blooms might occur again, however, all types of nuisance algae growth are more common in nutrient-enriched waters. Lake Champlain is certainly more vulnerable to having toxic blooms as long as phosphorous levels in the Lake remain high. As nutrient loads to Lake Champlain are reduced, algae blooms of all types should become less common.
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