Water quality monitoring has been an ongoing project of HLWA since 1996. Collecting data and charting it is as important to managing the health of the lake as having your blood analyzed for your personal health management. Our consulting limnologist, Dr. George Knoecklein, prepared a detailed report – “Highland Lake’s 2009 Monitoring Results.” The three aspects of monitoring are lake water quality, inlet stream sampling and aquatic plant survey. I will briefly review his findings.

Lake Water Quality
Lake water quality is primarily affected by the water clarity, dissolved oxygen and phosphorus content. Water clarity is an indicator of the overall health of a lake. The more silt, pollen, algae and other elements suspended in the water column, the less clear it is, less aesthetically pleasing and less healthy. Highland Lake undergoes a seasonal trend of increasing clarity from April through October; in April 2009 clarity was 11.2 feet, and in October it measured 14.4 feet as measured by a Secchi disc.

Spring arrived early this year and gave rise to a lot of pollen and heavy rains, which carried a good deal of silt into the water. However, the past two months have been extremely dry, and our August testing revealed some of the clearest water recently. Visibility in first bay was good to 13 feet, in second bay to 14.5 feet, and in third bay to 18 feet. This is a potent demonstration of how much silt and other debris is carried into the lake by rain events. Both surface and subsurface erosion as well as storm-drain runoff are a major factor in the clarity of our water and the filling of the lake with soil and nutrients.

Dissolved oxygen is very important to the health of a lake; fish and other aquatic life need it to survive, and oxygen in the lower depths of the lake helps keep phosphorus adhered to the sand/silt. Dr. Knoecklein reported that by August and September 2009, there was no oxygen below 22 feet in first bay, 35 feet in second bay and 25 feet in third bay. Thus, fish had a narrower band of water in which to survive, and phosphorus readings were higher at the lower levels of the water column. We are seeing a similar pattern for 2010; August monitoring revealed oxygen depletion below 23 feet in first bay, 43 feet in second bay and 26 feet in third bay.

Phosphorus content is the third important indicator of the lake health since it is the primary nutrient that feeds aquatic plants and algae. As Highland Lake ages, it experiences increasing levels of phosphorus. Many of you have reported seeing green, cloudlike formations near your waterfront. They are probably filamentous algae that grow in threadlike mats and are similar to cotton candy. The presence of this algae indicates nutrients such as phosphorus are retained close to the shore, particularly during a deep winter drawdown, and may grow filamentous algae after the lake refills. Also, disturbance of the lakebed during construction/maintenance of retaining walls or piers releases phosphorus. There was more work done this winter since a deep winter drawdown was conducted. Please keep in mind aquatic plants consume oxygen as they die and further add to the lakebed silt. We implore all watershed property owners to discontinue using fertilizer-containing phosphates. There are many natural lawn foods that contain no phosphate which can be located on the Internet. Also, reducing the size of your lawn by using ground covers and shrubs that don’t need fertilizer will reduce the amount of phosphorus in the lake.

Inlet Stream Sampling (2006-2009)
Dr. Knocklein was also employed to sample the major streams leading into Highland Lake in order to assess their water chemistry and impact on the lake. Sucker Brook, Taylor Brook and Platt Hill Brook are surrounded by a drainage area that makes up 75% of the overall watershed area of the lake (2,992 acres). Dr. Knocklein found a higher content of phosphorus in these streams than the overall lake. He returned last week to further examine the situation prior to making predictions or making recommendations.

Aquatic Plant Survey
Dr. Knocklein conducted a comprehensive plant survey over a three-day period in August 2009. He made observations and took samples at 278 sites less than 100 feet apart and in all depths of water where plants grow (up to 12 feet). He identified 31 plant species, four of which are invasive. The invasives are Eurasian milfoil, variable leafed milfoil, naiad minor and purple loosestrife. We have been applying Diquat in an effort to control the milfoil. However, this summer there was no money in the Town budget to cover the costly treatment.

Last week Dr. Knocklein conducted a follow-up survey of the areas where the invasive plants were growing. This is the first time we have had a survey conducted before and after a deep drawdown and after a summer with no herbicide treatment. I will report his findings as soon as they are available.