© Bennett & Fagon Lakes Association Water Quality Report, 2009 Season - Jane Brammer Water quality in our lakes is commonly understood in terms of how clear the water appears. Water clarity is influenced by the amount of phytoplankton or microscopic algae in the water.  Water clarity is measured with a Secchi Disc, a 20 cm black and white disk attached to a measured line, which is lowered into the lake until it is no longer visible.  Secchi disc results may range from 1m to 5 m depth, with lower numbers indicating lakes with more algae. The amount of algae in lakes is influenced by nutrients (plant food) in the water.  Phosphorus (P) is the nutrient of most interest in lakes, because P is usually the growth-limiting factor for algae and plants.  Total phosphorus (TP) in water is measured by laboratory testing of water samples. The Provincial Water Quality Objective for TP is 20 micrograms / litre (ug/L).  When TP concentrations are routinely greater than micrograms/litre (20 μg / L) in a lake, profuse plant growth can be expected to occur. Water quality sampling was done on Bennett and Fagan Lakes once in 2009 (17 August 2009), by enthusiastic local volunteers.  Surface samples were taken at 10 locations - 2 in Fagan Lake, 6 in Bennett Lake, and 1 in each of the primary inflow and outflow areas.  Depth samples were taken in 3 locations – 1 in Fagan Lake and 2 in Bennett Lake. Secchi disc readings in August 2009 at 3 deep water locations were from 3.2m depth to 3.7m depth, indicating moderately enriched lakes. Total phosphorus (TP) concentrations in August 2009 ranged from 8.2 to 15.7 ug / L.   Most samples (85%) were greater than 10 ug / L and less than 20 ug / L, indicating moderately enriched lakes. No samples had TP over 20 ug / L, whereas in 2008 water sampling in October, 31% of samples were over 20 ug / L.  The higher levels in 2008 are most likely associated with different sampling dates (October instead of August).  However, variability in results may also occur because of other factors - different temperature and rainfall conditions between years, variability inherent in the measurement, and varying nutrient inputs. In August 2009, depth sample phosphorus results were similar in value to surface water sample, suggesting little phosphorus input from lake sediment at the time of sampling.  This is good, because phosphorus in lake sediment can be released into lake water under certain conditions, and can push a lake into sudden algal blooms. Another water quality issue is oxygen levels in deep water.  Decaying algae and vegetation on the lake bottom use the available oxygen necessary to sustain aquatic life in the lower portion of a lake.  Dissolved oxygen data measured at the deepest point in Bennett Lake in August 2009 showed oxygen levels below 5% at depths greater than 7 meters.  Fish and most other aquatic like cannot survive under these conditions.  The other 2 deep water sampling points (5m and 6m depth respectively) showed oxygen levels over 20% at depth. In summary, water quality indicators in 2009 continue to show our lakes to be moderately enriched, and prone to late summer anoxic (low oxygen) conditions in deep water.  Residents and visitors to Bennett and Fagan Lakes must be vigilant in their efforts to protect the lake from nutrient loadings. What must be done?     Use and maintain your septic system according to manufacturer’s instructions.  Have your sewage pumped off-site every three years.     Preserve natural shorelines and natural vegetation, especially in shallow water and the first 10m of shore.  Avoid shoreline damage or removal of natural shoreline vegetation.     Do not use plant fertilizers of any kind on your site.     Restore cleared areas by planting native species.     Do not use phosphate-containing household products (dishwasher detergent, other soaps and cleaning agents).  There are more suitable substitutes available.