Salem Has Started the Switchover from Canobie Lake to Arlington Pond
Every fall, Salem stops taking drinking water from Canobie Lake and switches to Arlington Pond. In spring, it switches back. If you are new to the lake, this yearly switch explains why our water level rises and falls the way it does.
Salem's two bodies of water
Canobie Lake has supplied Salem's water since 1903. The lake is full at about 220 feet above sea level. That is the top of the flashboards on the dam.
In the winter of 1995 to 1996, the lake fell to about 212 feet. Docks sat on dry ground. The state stepped in. In February 1996, the NH Department of Environmental Services (NHDES) ordered Salem to save water and find another source.
Salem's answer was Arlington Pond, also called Arlington Mill Reservoir. In 1997, Salem completed a pipe that carries Arlington water to the Canobie Lake treatment plant. Since then, Salem draws from Arlington in the colder months. That gives Canobie time to refill from fall rain and spring snowmelt.
It worked. CLPA's records show the lake has run about two to three feet higher since 1997 than before. Salem also now buys water from the Southern NH Regional Water pipeline.
What the Arlington Pond Agreement says
The agreement limits when Salem may take water from Arlington Pond. It does not specify when Salem must start. The Town of Salem and the Arlington Pond Protective Association signed it on March 14, 1996. It protects boating and shoreline use on Arlington Pond, and it runs until March 14, 2046.
The agreement requires Salem to use its "best efforts" to raise Arlington to 161.712 feet by April 30 each year. The top of the spillway at Arlington's Wheeler Dam is 160 feet.
Here is what that means in plain terms:
October 11 is the first day Salem may begin the switchover procedures. It is a starting gate, not a deadline. The agreement does not require Salem to be on Arlington by any date in the fall.
April 30 is a firm stop. Salem must be back on Canobie by then, unless Arlington is unusually high. Arlington must be at 161.7 by April 30, or withdrawals must stop. This is the first year in my knowledge that Arlington was not at or higher than 161.7 by April 30
The agreement allows Salem to utilize Arlington Pond to give Canobie Lake time to recharge over the winter months.
How the switch works
Salem lowers Arlington Pond to its winter level first, then moves its water intake from Canobie to Arlington. In past years, the steps have looked like this:
Notice to Arlington residents. Salem tells boaters on Arlington to pull their boats before the water drops. That was done on Oct. 9, with notice that it would start Oct. 11.
Arlington drawdown. Salem opens the gates at Wheeler Dam and lets water flow down the Spicket River. In 2010, Salem lowered the pond about 5 feet, to a winter level near 156 feet. Lower water keeps winter ice from crushing docks, and it gives owners a window for permitted dock and beach work. The lake is lowered to 156 msl every year
Room for upstream water. Derry lowers Big Island Pond in the fall, and that water flows into Arlington. Salem times its own release so Arlington can take that extra water.
The switch. Once Arlington reaches its winter level, Salem starts pumping Arlington water to the treatment plant and stops drawing from Canobie. The transfer begins after water quality testing has been completed in compliance with our Cyanobacteria Monitoring and Response Plan
Winter recovery. Canobie normally refills from fall rain and spring snowmelt. Most of the lake's yearly refill happens between leaf-fall in October and the spring melt.
Spring return. Salem normally goes back to Canobie by April 30 and lets Arlington refill from the flow of Big Island Pond. If Arlington Pond is at a level of 161.7 or higher we can stay on Arlington as long as water quality allows.
What happens at the treatment plant? Why can't they switch in a day?
Transitioning raw water sources requires technical recalibration at the Water Treatment Plant:
Water chemistry monitoring. Raw water chemistry in Arlington Pond differs from Canobie Lake (for example, variation in organic loading, turbidity, pH, and algae levels). Water treatment operators perform jar testing and continuous monitoring to adjust coagulation, flocculation, and disinfection chemical dosages.
Flushing and switching valves. Operators isolate the raw water intake valves from Canobie Lake and open transmission lines connected to the Arlington Pond Pump Station. Operators systematically flush the lines to ensure drinking water standards set by the EPA and state regulations are maintained.
Two things can delay the switch. One is water quality. For example, cyanobacteria (blue-green algae) near the Arlington intake pushed the switch later. The other is Salem's own operating schedule, which the agreement leaves up to the Town.
Where things stand this fall
Salem began lowering Arlington Pond on October 11, the first day the agreement allows. Salem will be off Canobie Lake, and it is now scheduled to use Arlington Pond on November 1. That is earlier than expected. At the September 28 Town Council meeting, Salem's Water Department had said it would start on October 30 and finish the switch around November 15. The earlier start is good news for Canobie. Salem stops drawing from Canobie once Arlington reaches its winter level, so the sooner the drawdown begins, the sooner Canobie gets a rest.
NHDES agrees that timing matters. Brandon Kernen of the NHDES Drinking Water and Groundwater Bureau spoke with the CLPA President and is encouraging Salem to switch to Arlington Pond as soon as possible. The goal is to give Canobie Lake as much recharge time as possible before Salem switches back on April 30.
As CLPA President, I have attended several Salem Town Council meetings to encourage the switch to Arlington Pond as quickly as possible. The Town Councilors are taking the lake levels seriously. They are also weighing what each body of water issues, because a faster switch affects Arlington Pond's residents, docks, and water quality, not just Canobie Lake.
The lake is low. Salem's weekly reports show:
215.69 feet on October 16, which is 4.31 feet below full.
That is the lowest reading in Salem's weekly reports. The prior low was 215.89 feet on November 28, 2022.
The lake has dropped 3.07 feet since its May 1 peak.
On October 2, 2.71 inches of rain raised the lake only 0.09 feet. The 2.71” rainfall amount was over a 7-day period. The following week, we recorded only 0.18 inches of rain.
You may have heard two things that sound like they disagree. In August, CLPA said the lake is not at a historic low. Salem's weekly reports now show new lows. Both are true. CLPA's record goes back to 1989, and the lowest point in that record was about 212 feet in 1995 to 1996. Salem's weekly reports cover a much shorter period. A new low in those reports is still a real warning sign, and the Board takes it seriously.
The lake also did not refill last winter. That has now happened twice in about ten years, in 2016 and in 2026. Every extra week on Canobie this fall cuts into the winter recovery the lake badly needs.
What you can do
The switch date matters, but it only moves a few weeks of water. The lasting fix is finishing Phase 2 of the Southern NH Regional Water pipeline. Phase 1 already sends Salem all it can at summer peak. Phase 2 would add about two million gallons a day that does not come out of Canobie Lake.
Sign up for CLPA emails at canobielake.org/news/snhrwl. You do not have to be a member.
Read the Annual Meeting handout on the pipeline at canobielake.org/news/snhrwl.
Watch Salem Town Council meetings. That is where Salem reports its water plans.
Speak up when the pipeline bill is filed. Many households writing at the same time carry far more weight than one letter.
Questions? Write to info@canobielake.org.