De-Icing Theory and Practice

This article was authored by Paul Goodwin of Watermark Marine Systems, LLC, and was published in the Winter 2020 issue of the NH LAKES quarterly newsletter Lakeside.

There are a lot of myths and misconceptions regarding de-icing around docks, breakwaters, and boathouses during the winter months. First and foremost, everyone seems to call these units something different. I’ve heard bubbler, aerator, circulator, pump, aquatherm, and de-icer used interchangeably for as long as I can remember. In the end, they all mean the same thing: some sort of mechanical or electrical device to keep the freezing ice from wrecking waterfront structures.

Let’s review the theory and physical properties of de-icing around a dock. One of the unique properties of water is that as it starts to freeze, its density changes. Around 39 degrees Fahrenheit, water reaches its maximum density, creating a flip-flop effect that brings less dense, slightly warmer water to the lake surface. This occurs until all the water in the lake cools to 39 degrees. From there, the surface water continues to cool to 32 degrees (the point at which water is its least dense) and it expands to form ice. This is why lakes, ponds, and rivers freeze only on the surface and fish can survive in the relatively warm water below.

Ice damage caused by improper de-icing techniques. (Photo Credit: Watermark Marine Systems, LLC)

During the winter months, the ice expands and moves around. If a dock is frozen in the ice, it is likely to be damaged. If the water levels are low, and the ice rises due to rain and inflow, then pilings can be pulled out of the lake bottom. It is this combination of factors which causes the ‘ski jump’ type damage often seen on piling docks in the spring. The goal with de-icing is to open-up just enough water to keep structures disconnected from the ice sheet, but only enough to accomplish this separation.

It’s important to understand that a de-icer only prevents ice damage due to freezing expansion and water level changes. A de-icer does not protect a structure from large ice floes moving randomly around in the spring. Spring floe ice is best counteracted with ice protection pilings or by removing a dock. Some areas of our lakes are more regularly susceptible to ice floe damage from year to year. Of course, ‘ice out’ and the thawing process is not an exact science, so almost any structure can be at risk from ice floes.

Years ago, and this is the origin of the words ‘bubbler’ and ‘aerator,’ small air compressor pumps were used on docks during the freezing months and a garden hose-like pipe was wound around the structure, resting on the lake bottom. The air flow through the hose, which had numerous pin-holes along its length, allowed air bubbles to escape and race to the surface, bringing up warm water and causing weak spots or open water in the ice at the surface. These compressors ran non-stop and were relatively noisy. Neighbors were typically unhappy with the cumulative noise and often a cover was constructed to make them quieter. Covers could cause units to overheat and fail and, once the ice refroze, it was usually impossible to restore open water. One advantage of this type of unit was the relatively small amount of open water at the surface; however, as they ran constantly, they were not energy efficient.

This is an example of how to de-ice around a dock without creating an open water area that extends beyond the property. (Photo Credit: Watermark Marine Systems, LLC)

Most people today are probably more familiar with the propeller-type aerator units. These can be floating, hanging, bottom mounted, or dock mounted. These types of units can open an incredible amount of ice, if run constantly. These work by bringing relatively warm water up from the bottom and pushing it around the docks via the spinning propeller.

So, the question everyone asks is: what will work best for me? Unfortunately, there is no easy or correct answer. Each site is affected by freezing ice differently and one must consider a number of factors, such as, winter uses, sun exposure, currents, depth contours, prevailing winds, and other site specific factors to maximize efficiency and minimize too much open water. Do you like to snowmobile, ice fish, or skate and need safe access to the ice? Do you have a long dock, wide dock, or a special shorefront consideration? Are you around in the winter to monitor the ice? All these factors must be considered in choosing your best alternative.

We suggest having someone available to monitor your ice protection gear and starting out with either a bottom mount circulator in shallow water and a hanging unit in deeper water. By actively managing the circulators during the changing season, you can control the amount of open water and electricity used. Using a timer and a thermostat will allow you to accurately regulate the open water around your dock. Every site is unique. Through some simple experimentation and intelligent management of your ice protection gear, you can custom tune de-icing to your specific conditions without stirring up sediment or undermining structures. You will save a considerable amount of electricity and reduce the amount of open water around your shoreline structures, too!

BE ADVISED:  If you operate a de-icing unit…Effective July 14, 2019, the New Hampshire Legislature passed House Bill 668 which amended RSA 270:33. This amendment restricts the placement and operation of “aquatherms” to limit open water to directly in front of a lakefront owner’s property. Additionally, “THIN ICE” signs must be visible from ALL directions approaching the area, which means a minimum of three signs, arranged in a triangle so as to be visible from all angles.  As in the past, all shoreline de-icing equipment operation requires registration with the New Hampshire Department of Safety under RSA 270:34. Registration forms are available from your local Town or City Clerk for $0.50.

Volunteers Rock!

 “Volunteers don’t get paid; not because they’re worthless, but because they’re priceless”.

September 15, 2019 was truly a lovely Sunday afternoon in the Park; the perfect setting for a gathering of PLIA volunteers. Every fall the PLIA hosts a cookout at the Pawtuckaway State Park Pavilion to thank and celebrate its volunteers.

This year, President Tom Duffy recognized the hard work and tireless dedication of the folks who inspect boats in the Lake Host Program, look for invasive species in the WeedWatchers, gather lake and tributary water samples in the Water Testing program, search for and root out milfoil in the Milfoil Patrol, and pick up trash on Route 156 in the Clean and Scenic Road Cleanup Program. He also gave a shout out to the volunteers who run the organization, all year long.

Finally, Tom announced a very successful fund raising event that took place on Saturday, September 14, known as Paddle Poker. It was put together with the enthusiasm, energy, and dedication of a well-coordinated group of volunteers. And participants had loads of fun!

The PLIA appreciates that it could not not survive, and that none of its programs could operate, without the generous and spirited contributions of its volunteers. Everyone who treasures Pawtuckaway owes a debt of gratitude to these folks. Their hard work keeps the lake clean and healthy for all of us to enjoy! So, the next time you meet one of these special people, give them a big THANK YOU!

State Announces 2019 Lake Drawdown Schedule

The New Hampshire Department of Environmental Services (NHDES) has announced that the annual fall drawdown of Pawtuckaway Lake will begin on October 14, 2019.  It is anticipated that the water level will be drawn down to 4.8 feet below full pool.
For a complete list of the lakes and ponds controlled by dams owned by NHDES and their scheduled drawdown dates, click
You can track the actual level of water in Pawtuckaway through the gauge that is located on Dolloff Dam which measures the level of lake water and other conditions in real time, by clicking here.
And for an informative discussion of how the water levels of Pawtuckaway Lake are managed, you can read this website’s article titled Lake Level.
So, no hurry–there will be enough water in the lake to enjoy your favorite activities for another month. Enjoy, and
See You on the Lake!

Support the Pawtuckaway Lake Improvement Association Through Amazon Smile!

Support the Pawtuckaway Lake Improvement Association Whenever You Shop!
Now you can make a donation to the PLIA when you buy anything through! Here’s how it works:
Just click on this link or go to
This will take you directly to in support of the Pawtuckaway Lake Improvement Association. You can save this to your favorites or bookmark it so that whenever you decide to shop through Amazon, you can use this site and be sure that your purchases trigger an automatic donation from Amazon to the PLIA. You don’t even have to think about it and it costs nothing!
Each actual donation may be small, but they add up over time and so when you shop, Amazon donates. It’s a painless way to help the organization that protects the lake you love.
Pawtuckaway Lake thanks you; we thank you!

New Milfoil Divers on the Lake!

On Saturday July 6th, three open water certified SCUBA divers were trained and certified in exotic milfoil weed removal. We now have FOUR Pawtuckaway divers to remove milfoil when we find it!

FINDING the new growths of variable milfoil is the hard part of this important work.  Our team of snorkelers has been working overtime in search of new plants and growths. Once plants are found and identified, they are marked with floating markers. Then the divers know where to find the plants for removal.

In addition, we trained three topside “tenders” in kayaks who assist the divers to maximize their underwater time for search and removal. We need to train more of these topside tenders to protect the divers and snorkel search teams from wayward boaters, keep them supplied with tools and materials, and cart off the removed plants.  It’s a big job! In the photo below you will note the “diver down” flags strategically placed to indicate where divers are located.












In the last week we have logged over 60 hours in volunteer time on this most important mission.

Special thanks to Ted Aldrich ( who made the trip from Keene to train our volunteers for an 8 hour day!

Thanks to all our members who support our Lake Host and Weed Control Programs with your higher level dues donations.  It helps our reimbursement for materials, supplies, and training.

If you are interested in these volunteer activities, please contact us at

A Good Time at the PLIA’s Annual Meeting Saturday June 8

Record numbers of members attended the Annual Meeting of the PLIA on June 8, 2019, at the Pawtuckaway State Park Pavilion. Following coffee and refreshments, there was time to circulate and socialize, review the reports of Program Chairs, meet new neighbors and members, and scan the recently published updated Welcome Booklet. President Tom Duffy reflected on the PLIA’s activities and accomplishments in 2018, then Membership Chair Mike Coltin presented the 2018 Local Hero Award to Dee Decker, longtime PLIA member and volunteer. Dee was honored for her tireless work as coordinator for NH LAKES’s Lake Host program at Pawtuckaway Lake. She organizes volunteers, obtains funding, does trainings, recruits Lake Hosts, schedules shifts, compiles data and reports on boat inspections, advocates for lake healthy policies and laws, and steers our program into the success it has become. Whew! Weed Watcher Co-Chair Steve Soreff introduced our speakers from the Marine Patrol. Their talk was highly informative and engaging. The audience had many questions which the Officers answered with insight and good humor. Following a light lunch, some members opted to take a pontoon boat ride with President Tom Duffy, Water Sampler Jim Kelly, and Milfoil Team Leader Neil Santos to learn more about our Water Testing and Milfoil Management Programs.  

What’s In It For Me?

At the PLIA Annual Meeting on June 8th at 9:30 AM– just fun, information, refreshment, games, T-shirts, conversation, enthusiasm, community spirit, celebration, exploration, education, and environmental awareness—that’s all!

First off, some games to keep the kids busy while the grownups attend to more serious business under the shelter of the State ParkPavilion. Corn hole, ladder ball, or can jam, anyone?

The weather seems to be cooperating (so far), and that means one of our Board members will be leading a guided hike after a light lunch to take advantage of the beautiful trails in Pawtuckaway State Park.

For others, we will be offering a trip to the Park Camp Store for those who want to sample its wares, then an excursion on pontoon boats to learn more about our Water Testing and Milfoil Management Programs.

We have reserved the Pavilion at the State Park for the entire day! Entry for our Annual Meeting is free! Check out this map that highlights these events near the Pavilion where our meeting is taking place:

Let’s make this a banner year for Annual Meeting attendance! You don’t need to be a member if you want to come and learn about our organization. Neighbors and friends are welcome.

Just Say, “I’m with the PLIA”

The PLIA’s Annual Meeting this year is at the Pawtuckaway State Park Pavilion. Entry for this event is free of charge! Please join us, and bring the kids:

Saturday, June 8th

9:30 AM

State Park Pavilion

As you drive up to the State Park entrance, just say to the attendant in the booth, “I’m with the PLIA” and they will wave you through. There will be a sign at the place where you turn off the main park road into the parking lot for the Pavilion, about 1.3 miles down the road to the right.

There will be coffee and refreshments, games to occupy the kids, and after the meeting, a light lunch. If you stay and the weather cooperates, there will be boat rides and hikes, too!

The State Park is Hosting the PLIA’s Annual Meeting on June 8, 2019 at 9:30 AM at its Pavilion—Bring the Kids and Stay for a Light Lunch, Too!

Every spring, the PLIA holds its Annual Meeting. Existing members, renewing members, and newcomers to the lake are all welcome to attend this event. It has many purposes:

  • to vote on new Board members and conduct other business,
  • to bring everyone up to date on the achievements and goals of the PLIA,
  • to encourage discussion and debate about lake stewardship,
  • to foster the spirit of volunteerism,
  • to celebrate the benefits of membership, and
  • to provide a venue for members to socialize or meet new neighbors.

This year, we are happy to announce that Pawtuckaway State Park is making its Pavilion available to us as the location for our Annual Meeting. Entry to the Park for this event is FREE OF CHARGE!

Our long-standing neighbor to the west, the State Park is also a valuable partner in one of our most important programs; namely, the prevention of the introduction of invasive aquatic species into the lake. They have trained their staff about invasive aquatic species and the mission of NH LAKES’s Lake Host Program. They have welcomed our Lake Hosts into the Park to perform courtesy watercraft inspections, take surveys of visitors to the Park, and spread the alarm about milfoil.

Now they are welcoming us all to enjoy the beauty of the State Park while we conduct the business and pleasure of our Annual Meeting. Stay tuned for more details in the coming weeks (Games! Demonstrations! Boat Rides! Hikes!)

And meanwhile, heartfelt thanks to the NH Division of Parks and Recreation!

Volunteer Lake Host Training

Hosted by Dee Decker
May 22nd 9 AM – 1 PM
Conference Room 1, Nottingham Town Offices
139 Stage Road, Nottingham
NH LAKES is providing training by webinar this year! We will be watching the webinar together and then a pre-recorded message from Amy Smagula at NH DES. Dee will also be updating volunteers on Signup Genius scheduling. Weed Watchers are welcome to attend as well, or anyone with a boat or boat ramp in New Hampshire.
Lake Host volunteers who are unable to attend are welcome to sign up for one of the other  webinars using this link: Training Requirements, Dates, and Registration.