The Public Works and Parks, Recreation and Cultural departments have been working with the Crystal Lake Conservancy to study and monitor the watershed inputs and water quality of Crystal Lake for nearly a decade. This collaboration has allowed our Department to fast track the development of the Crystal Lake Watershed Management Plan, completed in January 2020. Recommendations in the Plan include more frequent street sweeping, design and implementation of stormwater best management practices (i.e., infiltration systems to reduce stormwater runoff and/or rain gardens) and addressing internal lake contributions. A primary finding in the Plan is that internal recycling of nutrients (phosphorus) found in the sediment of the deepest areas of the lake are a major source of algal blooms.
Our lake expert recommended we inactivate the phosphorus in the sediments with a low dose of aluminum sulfate (35 grams per m2) for roughly 10 acres or one-third of the total lake area. After presenting the Plan to several stakeholder groups, including the Crystal Lake Working Group and Parks & Recreation Commission, we obtained permits from the MaDEP and Newton Conservation Commission to proceed with the water quality treatment.
On Friday, May 8, 2020, we successfully completed the first of two recommended treatments. The initial results are very promising. Pre-treatment monitoring on May 7th showed visible algae in the water column and rising pH levels, fairly high for mid-spring. Post-treatment monitoring shows increased water clarity (from 9.5 to 16.4 feet), increased dissolved oxygen at the lake bottom (from 37% to 59%) and normalized pH levels (from 7.9 to 6.8).
We will be monitoring the lake throughout the summer and into the fall to ensure project success.
The 2nd phosphorus treatment will be completed two years from now (May 2022). In the meantime, we will continue our efforts to reduce phosphorus and sediment from entering the lake and work with stakeholders to increase public awareness on the benefits of lake stewardship.