The naming protocols for labeling bodies of water have changed frequently over the years. Most people believe it has to do with the area of the lake. i.e. if the area of water is large it must be a lake. However, the current naming protocol is a combination of historical usage and how deep the average depth of the lake is. If the water depth exceeds 25 feet on average (Thomas Pond average is 22')  then it is referred to as a lake; anything else is a pond.

The majority of water added to Thomas Pond comes from precipitation.  The drainage area for the pond is relatively small at ~5.5 acres.  Many lakes and ponds in Maine have a prominent source such as a river or large stream. For example, Sebago Lake has several rivers flowing into it such as the Songo River, Muddy River, and the Crooked River. However, Thomas Pond has only small surface creeks or streams flowing into it all around the perimeter of the pond. Rainfall also feeds the ground water table affecting everyone’s wells and the seeps that also help fill the pond. These are often referred to as “springs” and if you swim any distance in the pond you will quickly discover how prominent they are by the cooler water temperature you swim through.

Water leaves Thomas Pond in a variety of ways.  Most obvious is by discharge over or through the dam into Dingley Brook and then into Sebago Lake.  Water also leaves the pond by (a) evaporation, (b) absorption into the groundwater and (c) ingestion and use by plants, and (d) use by humans.  We don't have great details on the amount of water used in each of these ways, other than the amount released over the dam.  However, DEP estimated that the pond will lose roughly 5 times as much water through evaporation in the summer as it will through releasing 3" of water over the dam.

TPIA is required to release a minimum amount of water over or through the dam equal to the Aquatic Base Flow (ABF) of Thomas Pond at the dam.  This is an estimated value based on the median August flow, since no one conducted a detailed study required to directly measure the ABF of Dingley Brook prior to construction of the dam. 

At the time of the transfer of the dam to TPIA in 1990 the ABF was estimated by US Fish & Wildlife Service as 2.4 cubic feet/second (cf/s).  Subsequently Maine DEP determined that this number was too high and new calculations were developed in 2015 that estimated that the ABF for Thomas Pond at the dam is actually 1.18 cf/s, and this is the amount TPIA is required to release.  There is a great online tool, StreamStats, provided by the US Geological Service that can be used to calculate the ABF.

There is a small (6 feet in width) water control device equipped with stop logs— 4 X 4s that are dropped into a slot in the concrete dam that holds back the water flowing into Dingley Brook to Sebago Lake.  

We have a Management Plan for the Pond that was developed by Thomas Pond Improvement Association that tells the Dam Keeper the minimum and maximum flows and at what level the water should be maintained depending upon the time of year. For the Summer months, when most people want to enjoy their waterfront property, the Plan says to keep the water level between 17 and 20 inches as measured from the top of the dam.  That narrow band of water levels allows folks located at the extreme northern and southern ends of the lake to have sufficient water so that they can wade or launch a kayak. That same plan, and the Board Order that transferred ownership of the Dam to TPIA, require release of the Aquatic Base Flow, estimated at 1.2 cubic feet/second (~2 inch) flow over (or through) the dam at all times.

In the event a major storm is forecast and the water level is approaching or expected to exceed the upper limit of 17 inches, the Dam Keeper will take a stop log or two (3 1/2 inches each) out in anticipation of rising water. Once the event has passed and the rainfall is known, the stop logs are adjusted as needed after the rain has had an opportunity to flow into the pond.

In October, when water recreation has passed for the most part, the Dam Keeper will remove  stop logs allowing the lake level to recede to no more than 24 inches below the top of the dam, and typically to 26-28 inches below. In the Spring in anticipation of snowmelt runoff, the stop logs will be judiciously replaced so as to maintain the minimum required flow, not flood the lake, and yet still “capture” enough water to gradually raise water levels to the targeted 17-20 inches.

The quality of the water is very good. We are blessed in that we do not have any commercial, industrial, or major agricultural  operations around the pond. Such activities disturb the soil or add contaminants that affect water quality. The water quality is tested monthly from Memorial Day to well after Labor Day by trained and certified volunteers. It is tested for clarity by Secchi Disk readings or how low can you lower an 8 inch circular disk with alternating quadrants painted black and white and still see it through an underwater scope. Temperature is measured with a digital probe with readings every meter from the surface to the deepest part of the pond, which for Thomas Pond is practically about 61 feet. The probe also measures the dissolved oxygen content at each level to ensure there is enough to support life. Finally, the phosphorous levels are checked once a year in August to see what the phosphorous loading is at the surface. The readings for Thomas Pond are fed into a database maintained by Lakes Region of Maine on all area lakes. Our numbers have been consistently good for as long as data has been recorded, however the 2023 phosphorous level was higher than previous years, and is concerning.

If, when you bought your property, it had trees and bushes between your cabin/home and the waterline, keep them in place. Cut as few as you can and still gain access to the water. Every piece of natural vegetation helps to retain the soil and minimizes runoff. If your lot is sloped toward to water use a zig zag route of your path to the water rather than a straight line downhill. There are several organizations that can give you good advice for free on how to do this including Lakes Environmental Association, Lake Stewards of Maine, and our own organization, TPIA. All have websites like this one.

If you inherited a lawn all the way to the waterline, do not use any fertilizer, especially any with phosphorus as an identified ingredient (usually the center number on the bag). If you did not get your septic system inspected as part of your home inspection at closing, consider having it inspected as soon as possible. If found deficient, have it repaired immediately. If you come from a place that has city sewers you are probably not used to many restrictions on what goes down the toilet. Here in the country while you are on a septic field, minimize any chemicals you put down the toilet and consider adding a package of ordinary active yeast down one toilet in the house each month to keep things fresh. In a year-round house, depending on how many house guests you have, have your septic system pumped out at least every other year. With a high guest loading, annual pump outs are recommended. Finally, consider joining TPIA as a Board member or Officer representing your road association or neighborhood. Only through constant vigilance and engagement can we keep our beautiful pond clean and safe while protecting everyone's investment.