Eagle Lake Property Owners' Association
......what you can do today
         to help preserve Eagle Lake for tomorrow
Tim & Jane Venus and Irv Dardick

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Copyright © 2016 & 2017
Eagle Lake Property Owners' Association
You arrive at the cottage one weekend or get up one morning and stroll to the
dock to find a number of green cotton candy-like accumulations in the near
shore water. It looks unsightly, but what is it and it is worrisome? This
occurred in one section at Curl's Bay in the late spring this year (Figure 1). The
simple answer; excessive growth of green algae. These are not harmful to
humans or our pets.

We are aware of blooms of blue-green
algae (really a form of photosynthetic
bacteria referred to as
Cyanobacteria)-some which have
secreted toxins-in the Rideau River
system and some local lakes, so it is to
be expected that any obvious
proliferation of algae will cause concern.
Such was the case in Curl's Bay this
year where multiple accumulations of
algae were evident from late May
through mid-June (Figure 1), but were
completely gone by Canada Day.
Fortunately our investigations indicate
this was the harmless green algae, not
the potentially toxic blue-green type
(blue-green algae blooms are typically
commoner in late summer and early

Figure 1. Numerous discrete over-growths of
green algae in Curl’s Bay in late May of 2016 with
portions at the surface of the water (arrows). At
the margins of the floating mass in the centre of
the image, the pale green of the submerged
accumulation of filamentous algae is evident.
Figure 2. Extensive shoreline-situated bloom of a toxin-
producing Cyanobacteria at Upper Rideau Lake in
September 2014. Note the diffuse nature of this overgrowth
of blue-green algae compared to the focal overgrowth of
green algae in Figure 1. Photograph courtesy of RVCA.
What causes excess proliferations of algae?
o   Everyone thinks of poorly maintained septic tanks causing increased algae and that
can certainly be true, but other factors can also contribute. (Water samples from Curl’s
Bay in recent years have been well within normal limits.)
o   Excess populations of common algae naturally occur in the spring when there are
more nutrients (phosphates) in the water. As the nutrients are reduced the algae
subside. We had a hot May and June which might have stimulated the growth of algae.
Also, the lake water level was dropped quickly in mid-May and excess production of
green algae primarily occurs in shallow water in bays and along shorelines.
o   Significant soil erosion due to boat wakes and particularly due to the water level
fluctuations caused by the beaver dams at the train trestle adds extra nutrients to the
water which will increase algae growth.
o   Because Eagle Lake is mostly granite (Canadian Shield) it is naturally low in
phosphate, but good attention to septic tanks and soil erosion is still needed.
Still, were such algal masses in Curl’s Bay of concern? The myriad forms of algae and
diatoms are normal inhabitants of lakes and are, in fact, a vital part of the aquatic food
chain. Although there are a considerable variety of algae at Eagle Lake, the main
variety likely to produce a “bloom” are the filamentous types of green algae. These
occur as long thread-like structures composed of cells joined end-to-end. Since some
forms of blue-green algae (Cyanobacteria) can also form filaments, it is essential to
differentiate these two categories. General observations of how the two types appear
in lake water, as well as microscopic features, assist in distinguishing between the
green and blue-green algae.
The general appearance of the near shore
water assists in differentiating “blooms”
of green and blue-green algae. The “pea-
soup” appearance resulting from an
excessive proliferation of blue-green
algae occurs due to the organisms’ even
distribution throughout the depth of the
water at the shoreline (Figure 2). In
contrast, “blooms” of green algae are
more focal and even if they reach the
surface at multiple sites, there are still
patches of clear water in their vicinity
(Figure 1) and above and around
proliferations below the surface. Localized
accumulations of green algae below the
surface are common in spring and
summer, variable in size and can have a
compact gelatinous looking appearance.
Localized growths of green algae were common at Eagle Lake this summer due to the clarity of the water, numerous sunny days and warm surface water temperatures. At the site of the green algae proliferations at Curl’s Bay, three of the common filamentous forms of green algae were identified microscopically and photographed; these consisted of Spirogyra (Figure 3), Mougeotia (Figure 4), and Zygnema (Figure 5). At the Curl’s Bay site of excess green algae, Mougeotia was the dominant species.
Figure 5. Zygnema species. On the
left, a single filamentous strand
with individual cells each having a
paired internal structure. At
higher magnification on the right,
the cells of this species are seen to
each contain paired chloroplasts
with a characteristically stellate
Figure 4. Mougeotia species. The many intertwining
mesh of filaments of this species are considerably
narrower than the single filament of Spirogyra (on the
right in the left frame).  Each cell of this filamentous
species has a rectangular, platelike chlorophyll-
containing element with a clear space at either end of
the cell and a distinct cell wall (higher magnification
in right frame).
Figure 3. Spirogyra species. Three strands of this
filamentous algae, with cells arranged end-to-end, run
from top to bottom in the micrograph on the left.
Green pigment containing chloroplasts (the organelle
involved in photosynthesis) have a distinctive spiral
arrangement, more readily apparent at higher
magnification on the right, where the end plates
(arrows) of an individual cell are also seen.
There is an additional mechanism accounting for local algae becoming evident at the surface
(Figure 1). The photosynthetic pigment algae contain, chlorophyll, produces oxygen as a 
by-product during daylight. Some of this oxygen gets trapped within the mesh-work of algal
filaments making it buoyant. The result is a more obvious, but otherwise localized, green
algal “bloom.” Currently at Eagle Lake, some degree of algal proliferation is sporadic at
multiple sites of the shoreline, but has no long-term consequence or risk to the lake
environment or property owners.
There are undoubtedly many other unidentified forms of harmless green algae at Eagle
Lake, but this sampling should help reassure cottagers when typical accumulations of these
organisms are noted either below the surface or become sufficiently large and buoyant to
become evident at the surface. Furthermore, “blooms” of green algae are transient and do
not necessarily occur each season or in the same locales.