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1953 1976 1978 1991 2005
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      Water quality testing is an important diagnostic tool to help residents of Otter Lake determine the health of the lake. We need early warnings to predict important changes in the lake’s ecological process. By systematic testing and monitoring over time, it is possible to evaluate if water quality is improving or declining. By selective testing at strategic sites, water quality indicators can help determine the source or cause of contamination. The ecological and trophic status of a lake is generally determined by the levels of nutrients it contains.
      As in previous years OLLA was fortunate to have the assistance of the Rideau Valley Conservation Authority (RVCA) in testing the water quality of Otter Lake. Thanks are due to Sarah MacLeod-Neilson, and her qualified team of technologists for allowing us to include their data in this report. Both RVCA and OLLA test at least 3 times per year but at different sites. The map on the right indicates the location of all the current OLLA and RVCA test sites. These sites have been chosen to be representative of the whole lake. Sites 05A, O5B and 06 represent the 3 deepest water sites (more than 90ft). Sites 04, 07, 08, 11 and 18 are in areas where there are known inflows from streams and wetlands into the lake. Other sites are in shallow bays where there is an increased tendency for weed and algae growth.

      Recreational water quality can often be expressed in terms of how clear the water appears. Water clarity is influenced by the amount of soil sediment and phytoplankton, or microscopic algae, present in the water. Clarity is measured by a simple visual test using a Secchi Disk, a 20 centimeter black and white disk attached to a measured line. The disk is then lowered into the lake until it is no longer visible and the depth recorded. Additional information on water quality is gained through analysis of samples for nutrients, specifically phosphorus and nitrogen, which gives an indication of how much nutrient and energy is available for the growth of algae and aquatic plants
     Nitrogen in various forms is an abundant and essential nutrient in aquatic ecosystems. In addition to fertilizers, agricultural waste and wastewater contribute nitrogen into lakes. In large amounts, ammonia and nitrates can be toxic to aquatic organisms. Total Kjeldahl Nitrogen (TKN) which is what we and RVCA measure, determines the concentration of all forms of nitrogen in the lake. While there are no precise guidelines for acceptable levels of TKN, according to RVCA, TKN in water bodies not influenced by excessive organic inputs such as Otter Lake typically range from 100 to 500 µg/L.
      Phosphorous is generally recognized as the limiting nutrient in freshwater ecosystems and the major nutrient contributing to eutrophication in lakes. Since phosphorous is the principal source of energy for all living organisms the amount of phosphorous in the environment will determine how fast an organism grows and proliferates. Phosphorus is therefore the principal limiting factor in the growth of algae, meaning that algae growth will occur in greater amounts as more phosphorus is added to a lake. Most of the phosphorous that enters a septic system from phosphorous containing detergents will emerge intact, enter the water table and eventually the lake. Phosphorus levels below 5 µg/L are typical of oligotrophic lakes that generally are clear and deep with few nutrients. Such lakes are typically found in the northern regions of Ontario. Phosphorous levels above 20 µg/L are typical of eutrophic lakes that are laden with nutrients which lead to excessive algae and plant growth. Mesotrophic lakes have phosphorous concentrations between these two extremes and are typical of the lakes found in our region of Ontario
     Bacteria are present in all lakes, they will be found in the feces of the wildlife (fish, waterfowl, beavers, etc.) that inhabit the lake. Coliforms are bacteria found in the large intestine of humans and other mammals and are usually present in soil. While some strains of coliforms do produce toxins, most are not harmful to humans. Some such as Escherichia coli (E. Coli) do produce pathogenic toxins. Therefore levels of E. Coli are often used as indicators of possible contamination by fecal matter. Thus high E. Coli levels in lakes or rivers can be an indication of septic pollution. The recommended safety level of E. Coli in a lake for recreational safety is not more than 100 colony-forming units (cfu) per 100ml of water. E.coli at any level is unacceptable for drinking water, therefore some form of treatment and purification is necessary for anyone who draws water from the lake for drinking purposes.

RESULTS FOR 2018 - 219
      The table on the right indicates the results of all the water quality testing done in 2018 by OLLA and RVCA. Moderately high Total Coliforms were detectable at sites 04 and 07 in June. The latter site is close to Barker’s Creek, the major inflow into the lake and coliforms at this site are not uncommon since Barker’s Creek drains an extensive wetland and farming area west of highway 15. Low levels of E. coli were also detectable at this site, but were low at all other sites tested throughout the summer. It should be noted that a value of 2 cfu is the minimum detection limit for E. Coli.
      Total Kjeldahl Nitrogen levels were generally in the acceptable range of between 200 - 500 µg/L though site OLLA 04 was quite high in June for unknown. Phosphorous levels were all between 3 µg/L and 13 µg/L and there were no “hot spots” for phosphorous as were seen last year. Secchi depth readings were generally between 5.5 and 7 meters indicating that the lake remains very clear. Increased water clarity means that sunlight can penetrate deeper and may often result in algae blooms over the summer months however despite the higher than normal water temperatures no significant algae blooms were reported in 2018.
      Therefore with an average phosphorous level of 7 µg/L and an average Secchi depth of almost 6 meters the lake remains on the borderline between oligotrophic and mesotrophic but is overall closer to being oligotrophic. These results compare well with the data obtained in 2017 indicating that little is changing with respect to the water quality of Otter Lake. In fact Otter Lake has had total phosphorous levels around 10 µg/L for 15 years which means that Otter Lake's overall water quality is significantly better than any of the other lakes in the Eastern region of the Rideau Valley watershed. The reason is unknown, however possibly our extensive undeveloped wetlands are doing an excellent job of filtering inflow or perhaps we, as property owners are being environmentally conscious by limiting our use of phosphorous containing detergents and fertilizers!!
     The results of water testing in 2019 are shown on the left. They indicate that the trend seen in 2018 is continuing. E. coli was undetectable at most sites tested, but were moderately high in August at sites OLLA 03 and 09. Both these sites are shoreline locations in shallow bays at the North end of the lake. The reason for these higher than normal values are unknown, but these sites will be retested again in 2020. These values do NOT present a health hazard for swimming since in Ontario public beaches are closed only when E. coli levels exceed 100 cfu/100ml.
     Total Kjeldahl Nitrogen levels were generally in the acceptable range of between 200 - 500 µg/L, very similar to last year and only 3 test sites had total phosphorous values greater than 10 µg/L and the average for the year was less than 7 µg/L. Secchi depth readings were again about 6 metres indicating that the lake remains very clear but there were few algae blooms last Summer despite the hot weather.
     Therefore, Otter Lake remains very close to being classified as oligotrophic which is quite unusual for lakes in this area. Oligotrophic lakes are usually found much further North. As part of it;s Watershed Watch Program RVCA has put together a map of water quality (based on total phosphorous levels) of all the lakes in the Rideau valley catchment area that are surveyed annually. This map is shown on the right. Lakes with phosphorous levels of less than 10 µg/L are shown in light blue, 10 - 15 µg/L in light green, 15 - 20 µg/L in dark green and over 20 µg/L in red. As can be seen there are few lakes in light blue and Otter Lake is one of them. Click on the map to view in more detail.
     A printable version of this page is available here.

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.Site last updated - April 2020

History Board of Directors Policies Constitution Membership
1953 1976 1978 1991 2005
Important Contact Info Newsletters & AGM Minutes Lake Steward Reports Our Sponsors Articles of Interest