Resources

MLPOA partners with other Rindge lake organizations to work on water quality issues that affect us all.

Lake Contoocook | https://www.contoocooklake.org/
Mike Golibersuch | clapalake@gmail.com
The Contoocook Lake Area Preservation Association (CLAPA) is a non-profit 501c3 organization, to preserve the natural beauty and surrounding area of Contoocook Lake and its watershed. 

Pool Pond | https://www.facebook.com/search/top?q=pool%20pond%20protection%20association
Dave DelGiudice | D.delgiudice@comcast.net
Pool Pond Protection Association, a non profit, educates residents of responsible lakefront living, protecting from harmful invasive species and enhancing the water quality of Pool Pond. 

Dam: Controlling the Water Level of Lake Monomonac

At the time of this writing (fall of 2024), the MLPOA and WSLA are jointly proposing modifications to the operating equipment of the Great Dam. Replacing the existing flash boards with a new gate system is expected to improve the control of water flow and reduce the maintenance required by Winchendon DPW. A decision should be forth coming in the spring of 2025.

Lake Monomonac encompasses about 711 acres, 594 in Rindge NH and 183 in Winchendon MA. It has an average depth of about 11 feet, and is fed by many brooks and streams, the largest coming in from Converse Meadows.

The lake has two outlets, both in Winchendon. The first, known as the Great Dam, or main dam, is located at the southeast end of the lake. It is a 333 foot long earthen-embankment dam that is about 13 feet high and 28 feet wide at the crest. It has stone riprap on the lake-side face for erosion control. East Monomonac Road traverses the top of the dam. A concrete box culvert with flash boards, or stop logs, regulates how much water passes thru into Mirror Pond. The Red Dam controls flowage out of Mirror Pond.

The second outlet is the spillway, also referred to as the overflow or emergency spillway, at the southwest end of the lake. Located off the north side of West Monomonac Road near Route 202, it is a concrete weir of about 140 feet wide, equipped with flash boards to control water flow.

These two structures have traditionally been the primary hydraulic controls for the lake. The challenge thru the years has been releasing enough water to prevent flooding and maintaining the agreed upon lake height. The water rights, fall drawdowns, and summer heights have been controversial discussion points for many years and are beyond the scope of this article.

Lake Monomonac started out as a small river-like pond. Thru the years, its size increased after dams were constructed at the outlet leading to Miller’s River in Winchendon. One interesting note is that in 1800’s, Rindge was primarily a farming community, while Winchendon was actively pursuing manufacturing opportunities. In fact, in her booklet From Cotton to Cottages, Wilma Allen relates that the “Proprietors of Winchendon” encouraged people to build water-powered mills along rivers and streams, offering incentives such as 100 acres of land with the stream, to do so. As a result, Winchendon soon had mills for wood shingles, wooden toys, and textile products, among other things. The exact date of the first dam on Lake Monomonac is unknown, but in 1843 the mill owned by Springs Manufacturing in Winchendon Springs was offered for sale. Joseph White was the successful bidder and secured the building, dam, and flowage rights. White immediately set about expanding production and upgrading the area, including the mill pond and dams. His company, White Brothers, became one of the largest producers of dyed-cotton denim. It continued to operate until 1953 when economic factors forced its closure. Several years later (1958) White sold everything, including the dams and water rights, to Monomonac Lake Shores, Inc. Monomonac Lake Shores promptly raised the lake level and sold land lots in the Narrows and on what is referred to as Stump Pond. Little dam maintenance, however, was performed, as noted in the headline of the May 9th, 1968 edition of the Winchendon Currier: “Main dam owned by Monomonac Lake Shores rotting timbers — main gate might give way wiping out Spring Village.”

In October of 1972, Monomonac Lake Shores deeded the dams and water rights to the Town of Winchendon. Funds were donated ($1,500 each from MLPOA and the Town of Rindge, and $3,000 from the Town of Winchendon) for repairs to the main dam’s woodwork and for some excavation to improve water flow from the sluiceway. This effort, however, proved to be a stop-gap measure only, as water still could not be released fast enough during snow melt or heavy rainstorms.

In December of 1975, after severe flooding, the Town of Winchendon declared a limited State of Emergency when an inspection of the earthen dam indicated a possible collapse. Emergency work was performed by constructing a cofferdam around the site. A 30-inch ductile iron siphon pipe was installed and became the means of regulating water levels. Work was also performed at the overflow spillway on West Monomonac Road. The Town was rightfully praised for its rapid response to this emergency. However, this too proved only to be only a stop-gap measure. In June of 1984, a storm of over 5 inches of rainfall once again caused severe flooding.

The State of Massachusetts then authorized $200,000 in funding to reconstruct the emergency spillway and to upgrade the control structure of the main dam. Finally in 2004 a new dam was constructed, and is still in use today. Water levels are now dictated by an Order of Conditions from the Winchendon Conservation Commission with concurrence of the US Army Corps of Engineers. These conditions are renewed every three years. Presently, the lake is drawn down on October 15th and is refilled starting April 11th.

Lake Monomonac Resource Support – NH Department of Environmental Services (NHDES)

The MLPOA works in partnership with NHDES to help preserve and protect the health of our lake.

The NHDES Voluntary Lake Assessment Program (VLAP) is a statewide community and state effort to help the State of New Hampshire understand water quality trends in its more than 900 lakes and ponds. MLPOA participates in the VLAP program as a key part of its mission to protect and maintain the health and water quality of Lake Monomonac and has since its inception. Learn more

MLPOA follows their recommendations for Milfoil control. (2023 NHDES Milfoil Plan) The goal for Lake Monomonac is the reduction of overall biomass and distribution of variable milfoil in the system. We have treated specific areas of the lake chemically in the past and are now using divers to manually remove the smaller less dense plants that exist today. Today, only smaller/less dense areas exist.

Lake Monomonac LakeSmart Participants: As of 2025, 13 Lake Monomonac property owners have taken the LakeSmart Lake-Friendly Living Program’s self-assessment survey offered by NH LAKES. Of those, ten properties have had site visits, which resulted in two properties receiving the LakeSmart Award.

Want to learn more? Email your interest to lakesmart@nhlakes.org

The loon pair hatched one loonlet that year, but sadly, it did not survive. The pair did not nest again that season. The following year, spring of 2023, they nested on the same site, hatching two eggs. While both chicks hatched and were seen on the back of a parent, only one survived. It did well, and was seen well into that fall until it migrated to open water.

The pair returned in the spring of 2024 to once again nest at the same site. Even more, their one loonlet hatched on the same date as its “siblings” had years prior! This loon chick, too, did well and lived on the lake into the fall, when it migrated in December.