Indian Lake Closed May 28th and May 29th
The Indian Lake Watershed Association, in cooperation with The City of Worcester, has contracted with Aquatic Control Technology to conduct a treatment of Indian Lake with aluminum sulfate. The goal of the treatment is to lower phosphorus levels in the water and reduce the likelihood of nuisance algal blooms.
The treatment will take place on May 28th & 29th. On these days, we ask that you refrain from using the lake for swimming or other water contact activity beginning at 7am May 28th. Normal use may begin on Saturday, May 30th at 7am.
What is Alum?
Alum (aluminum sulfate) is a nontoxic material commonly used in water treatment plants to clarify drinking water. In lakes, a low dose alum treatment is used to strip the water column of phosphorus. At higher doses, it is often used to inactivate phosphorus in the bottom sediments. This is accomplished by applying an aluminum salt to the lake which reacts with the water to form an insoluble aluminum hydroxide solid (floc). This floc falls through the water column removing phosphorus and then settles to the bottom forming a "blanket".
The phosphorus which comes from external sources as well as the nutrients released from the sediment provides food for the algae.
In some cases, a higher level of Alum is used to seal areas of sediment that are releasing excessive nutrients prior to or in place of sediment removal. At this time only a low dose of Alum is being used at Indian Lake.
The practice of using Alum in surface waters has been around for 50+ years and has been utilized successfully on numerous projects in Massachusetts and around the country to lower phosphorus levels and reduce the frequency and severity of nuisance algae blooms.
How long will the Alum treatment last?
While many steps have been taken to decrease the nutrients in the lake, significantly more work is needed. An Alum treatment has been recommended for Indian Lake for many years but the cost has not made this possible.
A typical response to excessive algae is treatment with Copper Sulfate. This treatment is less expensive and kills the algae but could require multiple treatments as algae continues to bloom.
The Alum has a much better chance of getting us through the summer because it changes the conditions in the lake that make it such a great home to algae. There is no guarantee this will last all summer and we continue to fundraise for a Copper Sulfate treatment if needed.
We are fortunate to have many donors that stepped up to make what we feel is the best chance for success possible.
Where can I get more information?
There is a great document online that was developed by the Wisconsin Department of Natural Resources which is a good question/answer on the use of Alum to control phosphorus in lakes.
Wisconsin Dept of Natural Resources Alum Doc