Water quality testing is an important diagnostic tool to help residents of Otter Lake determine the health of the lake. 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 trophic status of a lake is an assessment of the enrichment levels contained in the water. Oligotrophic lakes are clear and deep with few nutrients. Eutrophic lakes are laden with nutrients which stimulate algae and plant growth. Mesotrophic lakes are in between these two extremes. Otter Lake generally exhibits the characteristics of a mesotrophic lake although the deep bathymetry of the central and southern areas of the lake is more typical of an oligotrophic lake. The development pressure is relatively high on Otter Lake with approximately 330 cottages, homes and commercial properties. As it relates to shoreline length, this is a much higher rate than other lakes in the Rideau Lakes area and indicates that factors such as septic system leaching, fertilizer application and shoreline erosion can have a greater collective impact. For the above reasons OLLA in conjunction with the Rideau Valley Conservation Authority RVCA) monitors water quality, notably coliform levels, phosphorous and nitrogen content and dissolved oxygen at least 3 to 5 times during the year at a number of test sites. The map on the right shows the location of the major OLLA test sites. Note that sites 05A, 05B and 06 represent the location of greatest water depth.
     The table on the right shows the results of all the water quality testing done in 2012 by OLLA and RVCA. E. coli was generally low or not detectable at all sites tested with the only exception being the slightly higher readings at OLLA 07 obtained in May and August. However, site 07 is where Barker’s Creek flows into the lake and since Barker's Creek drains an extensive area of wetland and agricultural land a higher E. coli reading at site 07 is not all that unusual.Total Kjeldahl Nitrogen levels were in the acceptable range of between 200 - 500 µg/L at all sites tested. Phosphorous levels were again quite low this year. There were very few readings greater than 10µg/L. Secchi depth readings were all above 5 metres, a little lowewr than the readings from last year, but they still indicate that the lake has excellent water clarity. However, increased water clarity means that sunlight can penetrate deeper and may often result in algae blooms over the summer months. While Otter Lake did experience some algae blooms in 2012, they were not as severe as they have been in previous years. The average phosphorous level of 6.9 µg/L (lower than last year) and an average Secchi depth of 6.5 metres indicates that the lake still remains on the borderline between oligotrophic and mesotrophic but is probably edging closer towards oligotrophic. The almost undetectable E. coli at all sites except Barker’s Creek indicates that the overall health of the lake is excellent.
     For comparison, the table below right shows the results of all testing performed in 2011. Total coliform levels were below 10cfu/100ml at all sites tested except at site 07 . This site is close to Highway 15 at the point where Barker's Creek flows into the lake. Higher than average E. Coli levels are usually recorded at this test site. Total Kjeldahl Nitrogen levels were all in the acceptable range of between 200 - 500 µg/L at all sites tested. Phosphorous levels were all quite low in 2011. The only reading greater than 10µg/L was at site 06 (a deep water site) that was tested by RVCA in September. Secchi depth readings (a measurement of water clarity) were between 6 and 8.5 metres, much higher than in previous years. The average phosphorous level of 8.11 µg/L and an average Secchi depth of greater than 6 meters would indicate that the lake remained on the borderline between oligotrophic and mesotrophic.
     In 2008 we tested for lead and found it to be virtually undetectable. In 2007 we tested for mercury, since in most Canadian fresh and marine waters, levels of total mercury (inorganic mercury plus methyl mercury and other organic forms) should be less than 20ng/L of water in Ontario and Quebec. However some considerably higher levels have been found in some areas. More information on mercury in lakes and rivers from the National Guidelines and Standards Office of Environment Canada is available here. Mercury levels were low or non detectable at the selected test sites in Otter Lake. As a result we have discontinued testing for these heavy metals.The complete water quality reports for previous years and the lake stewards reports which contain more details about testing and all results obtained, can be found on the Information-Lake Steward's Report page.
    In 2007 the Township of Rideau Lakes implemented a voluntary septic system re-inspection program. In all 100 homes and cottages in the township were scheduled for a re-inspection of there waste water disposal systems. Some of these would likely have been on Otter Lake.The re-inspection program report that was submitted to the Township by Jamie Saunders in January, 2007 is available here in PDF format. Note that the report is 30 pages in length, but does contain a lot of useful information. The Township reimplemented this program again in 2011 and several Otter Lake properties complied. No serious problems were reported.

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