Invasive Species & Cyanobacteria

We are fortunate to have very clean water in Great East Lake, and to date we have remained free from invasive aquatic plants. But with invasive species turning up in neighboring water bodies, we must remain ever vigilant, as the presence of invasive species could forever change the character of the lake. The other main threat to our water is the increasing presence and concentrations of cyanobacteria, which is highly toxic to humans and animals.


Aquatic Species

What are aquatic plants?

Aquatic plants are a natural part of the lake’s ecosystem and are important for a healthy lake. They provide habitat and food for fish and other animals as well as put oxygen back into the water. Native plants have evolved in balance with pathogens and herbivores. There are many species of native aquatic plants in Great East Lake and while the relative abundance of individual species may vary from year to year, the number of plants is quite low in most areas of the lake.


An overgrowth of aquatic plants can reduce sunlight penetration into the water, raise the pH to unhealthy levels and when the plants decay, dissolved oxygen levels can plummet resulting in fish kills. An overgrowth of aquatic plants can occur when there are elevated levels of phosphorus in a lake. Phosphorus is a key nutrient for plant growth and too much is damaging to the health of a lake.

There are steps that we can take to prevent or minimize phosphorus from entering the lake. For example, maintaining vegetative buffers around the lake and its tributaries, preventing soil from eroding into the lake or its tributaries, slowing down any run-off so the water has time to soak into the ground, not using fertilizer, and maintaining septic systems.

What are invasive aquatic plants?

While maintaining the health and balance of native aquatic plant species is important, it is also important to distinguish native species from invasive, non-native plant species. Plants become invasive when they are no longer controlled by natural pathogens and herbivores. One of the most infamous is Variable Milfoil, but there are many other invasive aquatic species that could do significant damage to Great East Lake if they were to be introduced and take hold.

Once an invasive species has taken residence in a water body, it is unlikely to be eliminated, only contained (and containment is costly). Invasive species can crowd out native species and habitats, eliminate areas for boating and recreation and adversely impact property values.

Where have invasive species been documented in Maine and New Hampshire?

Invasive species in NH

Invasive species in Maine

What can be done to protect Great East Lake from invasive aquatic plants?

Invasive species are typically brought by watercraft and/or their trailers as plant fragments or seeds. Once the seed or plant takes hold in the lake, it can quickly grow and multiply. The Lake Host courtesy boat inspection program and the Weed Watchers invasive plant survey program are important defenses against invasive aquatic plants, but you can help too.

Before and after boating:

  • Clean off any plants, animals, mud and other debris from your boat, trailer and recreational gear.
  • Wash and drain your boat (bilge, live wells and ballast tanks), trailer, and equipment away from the water.
  • Dry anything that came in contact with the water. At least five days drying time is best.

How can I report a suspicious plant?

Report a suspicious plant in Maine

Report a suspicious plant in NH

For more information:

How to identify Invasive Plants

Invasive aquatic plant guide from NH lakes

How to identify invasive species from ME DEP

Quick key to ruling out Maine’s eleven most unwanted invasive aquatic plants from MVLP



Cyanobacteria has been observed in the lake over time, but in recent years we are seeing it more frequently and at higher concentrations.

In August of 2022,the University of New Hampshire LLMP was performing routine water sampling in the lake. They reported that the Second Basin contained the cyanobacteria Planktothrix, that ranged from 100,000 cells/ml to too numerous to count in the visible clumps of varying sizes. Planktothrix at these levels can be toxic and also cause mild skin irritations. Planktothrix look like green or yellow green flecks of paint either on the surface or in the water column. A picture is to the right.

Also in August 2022,the Association received a report of a potential cyanobacteria bloom on the lakeshore along Canal Road. We took two samples and brought them to NH DES for analysis. They identified two cyanobacteria (Gloeotrichia and Doichospermum) as present in the samples at levels which were of concern. NH DES issued a Cyanobacteria Bloom Alert which GELIA posted on Facebook.

Gloeotrichia appear like whitish puff balls in the water column. It is common to observe low levels of Gloeotrichia in Great East Lake (and other low nutrient lakes) in the late summer.

In the fall of 2022, GELIA commissioned a report on the growing cyanobacteria problem in the lake, with recommendations on how we should continue to monitor and address the issues. A copy of the report is here.


Cyanobacteria Q & A

What are cyanobacteria?

Cyanobacteria are ancient, ubiquitous organisms. They were the first photosynthetic organisms and started the process producing our oxygen rich atmosphere. Wikipedia has more Cyanobacteria information

Why are cyanobacteria of concern?

Cyanobacteria produce an array of chemicals (called cyanotoxins) which are harmful to multiple organ systems. They can cause illness and death. However, research into the hazards of cyanobacteria is not well-funded and there is much that we do not yet know. Recently, Health Canada issued Guidelines for Canadian Recreational Water Quality, CYANOBACTERIA AND THEIR TOXINS This document provides a compilation of what is known and establishes safe levels for recreational water use (the accidental ingestion of a few ounces of water).

What causes cyanobacterial blooms?

Cyanobacteria are everywhere, typically at low levels. An increase in nutrients (phosphorous and nitrogen) and warm water can cause a bloom. A heavy rain can erode nutrient-containing sediments into the lake. This is one of the reasons why all waterfront properties should control erosion.

Do cyanobacteria “move around”?

Yes. They travel up and down through the water column and the wind can move them around a water body. It appears that the wind contributed to the accumulation of cyanobacteria for the Canal Road observation.

If I see cyanobacteria what should I do?

Keep pets and humans out of that water. Dogs, because they tend to lick the cyanobacteria off of their fur, frequently die from cyanotoxin exposure. Human illnesses and deaths appear to be rare but many ER doctors are not all well-trained to recognize poisoning by cyanotoxins.

If I see something of concern, can I get it tested?

Use a clean plastic container and collect water from where the cyanobacteria appear to be most concentrated (right off the surface if it is floating on the surface). After collection, keep the sample cool but DO NOT FREEZE. You will need to take it yourself to the New Hampshire DES lab in Concord. You can contact them at

Where can I get more information and who should I contact if I suspect there is a cyanobacteria bloom?

Both NH DES and Maine DEP have published information on cyanobacteria and how to contact them about cyanobacteria.

Can anything be done about this problem?

We don’t know yet. GELIA has supported a robust water quality sampling program for many years. It is possible that there are some answers in these data. In this regard, we have initiated a discussion with a limnologist.



Cynobacteria-Q & A

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