Otty Lake Association

Other Water Issues

Algae - Too Much of a Good Thing | Starving the Lake of Phosphorus   |   Water Levels   |   Shoreline Erosion |   Aquatic Plant Control

Algae - Too Much of a Good Thing

RIDEAU VALLEY, July 11, 2016 —  Have you noticed an excess of green algae on your lake or river this spring?

Algae and aquatic plants play an important role in maintaining the health of our waterbodies. But when you have too much — it can negatively impact recreational use and threaten our aquatic ecosystems.

Excessive algae and aquatic plant growth can have natural causes like warm water and air temperatures, early ice-off dates, strong sunlight exposure and extended periods of calm water. Quite often, excessive growth can be caused by high levels of available nutrients — both naturally occurring and man-made.

While we have little control over the natural causes of excessive algae growth, there a number of things landowners can do to make sure they are not contributing excess nutrients to our lakes and rivers: .

Let’s Starve Algae in Otty

Phosphorus MonsterAlgae - the Annual Loathsome Green Aquatic Eyesore. While this acronym isn’t a scientific description of the plague we experience every year, it does capture the prevailing sentiment about those ugly green blobs that appear at docks. Like all living things, algae need certain conditions to survive. They thrive in hot weather and prefer quiet water unaffected by wind. Algae also require nutrition, especially phosphorus.

To reduce or even rid Otty of the green slime we all hate there’s a simple solution - starve Otty of phosphorus run-off.

Water Levels

2010 Jebbs Creek

In July 2010 the Rideau Valley Conservation Authority completed a survey of the bed of Jebbs Creek along with a survey of the Creek water levels. The following Survey Comparison and Creek Profile provide a comparison with the previous survey of the bed of the creek done in 1983, along with the water levels.

Jebbs Creek 2010 Bed of Creek and Water Elevation Comparison (photo)
Jebbs Creek Bed of Creek and Water Elevation, Otty Lake to Tay Marsh (chart)


Water Levels and the Health of Otty Lake – March 2010

While some have expressed their concern about “high” water levels, others have been equally concerned about periods of “low” levels. There has been much discussion over the years, and the OLA has consulted with RVCA, MNR and Fisheries and Oceans to better understand what influences the water levels and health of Otty Lake.

Lake Water Levels and Lake Health

Lake water levels will not affect the rate of removal of nutrients from the lake . A complete exchange of the water from Otty Lake takes between 3 and 4.5 years. Hence the removal of nutrients in the lake has to be considered over this longer timeframe rather than on a seasonal basis.


The weather has significant impact on Otty Lake water levels. Hot, dry and windy weather can result in lower lake levels due to increased evaporation from the lake surface and reduced water input. When the weather is cool, overcast and rainy, lake levels are higher.

Otty lake green algaeGreen Algae

The “green slime” normally seen in the lake in the early summer is a form of algae. It is not caused by the lake needing to be able to flush itself through Jebbs Creek. It occurs when there is a lot of rain washing nutrients from the land into the water. It flourishes in the cooler damp weather we often have early in the year.


In 2009 the major land owners bordering Jebbs Creek regularly breached beaver dams and trapped beavers along their areas of the Creek. We understand that they will continue with this practice. However, Jebbs Creek is a natural habitat for beavers and beavers will regularly re-colonize a suitable waterway. We will continue to monitor what is happening in Jebbs Creek.

Impact on Shoreline Structures

Structures constructed during periods of low water levels will always be challenged in times of high water levels. As well, these structures harden the shoreline. Hardened shorelines deflect wave energy instead of absorbing it – the energy is deflected to the sides passing the erosion problem on to neighbouring sites and down, scouring away any sediment or plant life near the base of the wall. For docks with adjustable legs are recommended.

Impact on Trees

The Otty Lake Association is monitoring closely the potential impact of water levels on trees along the lake shoreline. For the most part, the higher water levels did not seem to be having a negative impact on the shoreline but we did document areas where trees were impacted and reported our observations to the RVCA. Monitoring of the lake shoreline will continue.

Regulatory (1:100 year) Flood Level for Otty Lake

An RVCA analysis, completed in 2011, attempted to estimate the 1:100 year flood level around Otty Lake, in order to provide a basis for RVCA's regulations re structure placement and flood proofing. Exact delineation was not possible due to the absence of full topographical data.


Shoreline Erosion

Erosion is a natural process, but it can be accelerated by human activity like the removal of shoreline vegetation or excessive boat wake. Natural vegetation along our shorelines plays a crucial role in preventing soil erosion, protecting water quality and preserving the ecological balance of aquatic environments. Without a healthy vegetated buffer, shorelines have reduced resistance against erosion.

Shorelinen Erosion HandbookA handbook is available to guide people on how to bring buffers back to their shore and fight erosion naturally. The Solutions for Shoreline Erosion Handbook goes beyond the traditional approaches to reduce erosion such as riprap or seawalls; it highlights options that use natural materials. Great for lakes, rivers, streams, creeks and drains across Eastern Ontario, the booklet shows different methods for different sites based on slopes, soils and space. It outlines the advantages and disadvantages of each method and includes contact information for agencies where permits and/or approvals might be necessary before starting a project.

Aquatic Plant Control

Aquatic plants are an important part of a natural aquatic ecosystem, especially in the ecology of shoreline areas. They provide habitat for fish to spawn, feed and hide from predators. Aquatic plants help maintain water quality by stabilizing sediments. But having too many aquatic plants can interfere with boating, swimming and other recreational water activities, and at times, some control may be necessary.

Regulations for Aquatic Plants

The beds of most water bodies in Ontario are legally public land. In order to remove aquatic plants by physical or mechanical methods, approvals from one or more agencies and a work permit from the applicable authority may be required. To obtain approval for in‐water and shoreline works in our area, your first contact should be the Rideau Valley Conservation Authority.

Control Methods for Aquatic Plants
  • Raking
  • Removal by hand
  • Mechanical harvesting
  • Cutter‐bar devices
  • Bottom barriers (mats or blankets)
  • Chemical methods (herbicides)

Week Raking from Boston GlobeTo preserve fish habitat, hand removal and raking are the preferred methods. Warm-water fish species spawn during spring and early summer, so do not remove aquatic vegetation during the timing moratorium, March 15 - June 30. Any plants removed should be disposed of well above the average high water mark.



MNR Regulations - Jan. 1, 2014


The Ministry of Natural Resources specifies rules for removing native aquatic plants that occur naturally in Ontario. As Otty Lake is south of the line indicated on their map, property owners or their agents are entitled to remove,  without a permit, aquatic vegetation in front of their property,  as specified in the regulations, provided that various conditions are met.  This applies to removal of aquatic vegetation by both hand and mechanical means.  The ministry specifies how wide an area you may clear depending on whether the width of your shoreline property is greater than or less than 22 m., and also allows for a boat channel if the weeds need to be cleared more than 30 m. from shore. A person also has the option of applying for  a work permit if the area to cleared is larger than the conditions described above.