Frequently asked water management questions

Trent-Severn Waterway National Historic Site

Always remember:

Swimming within 40 metres above, below or near dams is strictly prohibited. Undertow currents in these areas are extremely dangerous!

Everyone enjoys a long dry summer but what many don't realize is that it's a double edge sword. Appreciate those rainy days when they come – the rainfall keeps the lake levels up. The Trent-Severn watershed is highly dependent on Mother Nature to fuel the system....

What is water management?

Water management is the changing of water levels and water flows (volume/speed) by human actions throughout the Trent-Severn Waterway. This is done by:

  1. Collecting data;
  2. Analysing this data using models and tools that guide us in making decisions about changing water levels and flows;
  3. Adding or removing logs, or changing mechanized settings, in dams throughout the system.

Because these changes have an impact both upstream and downstream, as well as at the specific location where changes are made, water management is approached on a total system basis. In an area nearly four times the size of Prince Edward Island this includes:

  • Two main watersheds – The Trent River and the Severn River watersheds
  • 60 lakes (including subsidiary and flow through lake)
  • More than 250 marshes, swamps and other wetlands
  • 15 rivers
  • 102 operating dams
Why is water managed?

Water is managed for several reasons including:

  • Public safety including mitigation of flooding;
  • Protection of:
    • environment, fisheries, wildlife habitats
    • water supplies
    • navigation
    • recreation
    • hydro generation

The complexities of these multiple and interconnected considerations dictate the need to monitor and manage water on a full time basis, continuously throughout the year.

Who controls water levels for all the lakes and rivers along the Trent-Severn Waterway?

Parks Canada Trent-Severn Waterway manages water levels on the Trent-Severn Waterway and throughout the watershed with a few exceptions.

The Ontario Ministry of Natural Resources, local Conservation Authorities and hydro producers collaborate with Parks Canada.

Why do water levels and flows fluctuate?

Water levels and flows fluctuate for a number of reasons. Large amounts of rain, for instance, can cause lake levels to rise while extended periods of drought can have the reverse effect. Dam adjustments to re-balance water levels and flows may cause lakes to rise or drop while moving towards targets.

It is important to note that water levels are only one consideration and are intricately connected to flow rates. Certain flow rates are required at certain locations throughout the system to ensure water supplies and water quality are maintained. For example, we know that we must maintain a flow of 17 cubic meters per second (cms) at Lakefield in order to ensure a minimal flow of 5 cms at Trenton (Dam 1), and in order to ensure that 17 cms flow at Lakefield there must be a combined flow of 35 cms out of the Haliburton Lakes. These flows are required to maintain adequate water supplies for hydro generating stations, municipal water intakes and water quality throughout the system.

Sometimes water levels are lowered very early in the season. Why?

The lowering of water levels happens every year at the same time and is referred to as "drawdown". Water levels need to be lowered to make room for the precipitation that happens in the fall, winter and spring. In order to mitigate against flooding and optimize public safety throughout the interconnected system, lakes are lowered to make room for high inflows that are typical over the non-navigation seasons. Lakes in the system are subject to an equal percentage drawdown and in order to meet the targeted levels, this drawdown must begin by mid-summer. What happens to one lake or river is known to impact rivers and lakes both upstream and downstream.

It is also essential to have the water levels lowered prior to fish spawning as fish like to spawn close to the water’s edge in shallow areas. If the drawdown is done after eggs have been laid, the eggs will be exposed, dry up and die. It's important to protect the fishery in all lakes - as part of the ecosystem and an economic generator valued at more than $300 Million. Protecting fish habitat is also required under the Fisheries Act.

What is the drawdown?

Drawdown is when water levels are lowered in the Trent-Severn Watershed.

It's a complex process that takes into consideration storage capacity of the lakes on the system, timing of fishery spawning, requirements for flood mitigation, typical fall and winter precipitation levels, downstream typography including constrictions like narrow river beds or dams, and overall volumes and flow rates.

Drawdown is guided by research, engineering and decades of experience.

For lakes Simcoe and Couchiching a unique guideline, called a "rule curve," is used to guide the lowering of water levels to allow room for future winter snow melt and precipitation. Since these lakes are so large and the outflows so small relative to the volume of water, the drawdown must be carefully managed to mitigate flooding and protect public safety.

In the Haliburton reservoir lakes area, drawdown occurs throughout the summer season to address downstream needs along the Trent-Severn Waterway. Water levels are based on equal percentage drawdown as developed through collaboration with local community participants.

Why are some lakes called lakes reservoir lakes?

Some lakes were created by dams when the Waterway was constructed, to be reservoirs to provide adequate storage of water to be released as required over the navigation season. Every lake in the Haliburton reservoir lakes has been evaluated for its full volume to determine equal percentage drawdown water and flow levels.

What is equal percentage drawdown?

Equal percentage drawdown was developed in response to local wishes to make the drawdown fairer to all shoreline owners and users by distributing the impact of drawdown over as many lakes as possible.

Depending on the steepness of the shoreline the drawdown can make a difference to the appearance of water level changes. In other words, when the equal percentage drawdown has been applied to a gradual shoreline it will appear to have lost more water than a steep shoreline. If you think of a shallow shoreline as being like a nearly flat bowl, a half inch drop in water level will expose considerable more of the edge of the bowl than a half inch drop on a kitchen sink.

Why can't the drawdown of lakes be postponed?

There are many factors that guide the timing for drawdown and these will vary from lake to lake.

Public Safety and Flooding

Public safety and property can be severely and negatively impacted throughout the system if targeted levels and flows are not reached within a planned timeframe. For example, if larger bodies of water like Lake Simcoe and Couchiching are not drawn down in time, and there happens to be a lot of fall, winter and spring precipitation, sudden melt, freshet ice, high winds or heavy rains there is a high risk that low lying areas, like the Holland Marsh and many cottage shorelines could be flooded. This situation would risk public safety and property damage.


Large bodies of water like lakes Simcoe and Couchiching react slowly to climatic conditions and stop-log changes at dams than other parts of the system. Draining these large lakes is like draining a bathtub through the eye of a needle; it takes a long time. This factor affects the timing of drawdown not only for these bodies of water but for those connected lakes and rivers.

If drawdown was postponed and it started raining in September, downstream flooding could occur. By postponing there is an added risk that uncontrolled watercourses will contribute high volumes and flows and compound the public danger.

Environmental Considerations

Balancing water levels for spawning is another intricacy behind water management and the timing of fall drawdown. Because some fish species like to spawn close to the water's edge in shallow areas, if the drawdown is done after eggs have been laid, the eggs will be exposed, dry up and die. It's important to protect the fishery in all lakes - as part of the ecosystem and an economic generator valued at more than $300 Million. Protecting fish habitat is also required under the Fisheries Act.

Why is the water in some lakes so low (or so high)?

Water levels in some lakes may appear low or high for a variety of reasons. For example:

  • The lakes of the Trent-Severn watershed typically rise or refill in the spring depending upon the rate and volume of snow melt and spring rainfall.
  • During a typical summer the water stored from spring is gradually released to meet varying demands across the watershed influenced, in large part, by weather.
  • On lakes with a broad surface and shallow depth, evaporative losses over summer months typically exceed rainfall gains and water levels can drop for this reason. Conversely, when rains are heavy or winds are strong, levels can rise.

In addition to these natural factors, water levels are altered by dam log changes, the size and number of logs, the number of spillways and the number of dams affecting a body of water – the water management tool used to keep the system at targeted levels.

When will the water level be adjusted in certain lakes?

Water management happens all year long. Dam controlled water level adjustments to certain lakes depend upon conditions across the entire waterway. Think of the management of water levels as a domino effect; water level adjustments in one body of water impact the next, and so on.

Visit theWater levels to find out what’s happening in your lake in relation to the bigger picture, upstream and downstream of your location.

Where can I find out about the water levels for my lake and others?

You can find information about water levels by visiting Water levels.

How often is the online water levels report updated?

The online Water levels report is typically updated daily, excluding weekends and holidays.

What kind of technology does Parks Canada use to manage water levels?

Parks Canada has a system of water gauges, many of which are automated and produce data that tells us levels on various parts of the system. This is supplemented by many manual gauges, as well as data provided by Environment Canada on precipitation and weather patterns.

Historic data and seasonal patterns are also used as an important reference point. This data is then fed into a contemporary engineering water model and along with extensive waterway knowledge daily water changes are implemented accordingly.

Does Parks Canada update/maintain its water control structures and practices?

Yes. The Government of Canada has invested in significant improvements to water management in the last two years through the replacement of worn logs in Haliburton dams, the installation of hydrometric gauges throughout the watershed to gather water and weather data, and is undertaking ongoing research.

Can I get historical data for a specific body of water on the Trent-Severn Waterway?

Requests for historical data on the Trent-Severn Waterway are welcome. Please be aware, some historical data for the Trent-Severn Waterway is not computer accessible and therefore may take a considerable amount of time to obtain.

Requests may be forwarded to: Please allow time for a response.

What is a freshet?

The dictionary definition of freshet (a noun) is "a sudden overflow of a stream resulting from a heavy rain or a thaw." The term is used in reference to water levels rising due to melting snow and rainfall.

What is frazil ice?

Crystals of flowing ice that form together into a larger mass are referred to as frazil ice (also known as slush ice because of its appearance).

Two contributing factors behind frazil ice formation are cold temperatures and high river flow, particularly in turbulent areas, like dams. The accumulation of frazil ice in winter and early spring can create a natural dam effect inhibiting the flow of water.

What is the Water Management Advisory Council?

Parks Canada established the Water Management Advisory Council as part of the Government's Action Plan in response to the Panel on The Future of the Trent-Severn Waterway. The role of the council is to provide expert and stakeholder advice on how to best achieve its water management goals throughout the Trent-Severn watershed.

The council is led by an independent chair and consists of water management experts from:

  • Ontario Ministry of Natural Resources;
  • Environment Canada and Conservation Authorities;
  • Citizens from the Haliburton, Severn, Kawartha and Trent River watershed area;
  • Representatives from industry including the Ontario Waterpower Association and the Ontario Boating Forum;
  • Representation from the Trent-Severn Waterway (TSW).
How often does the Water Management Advisory Council meet?

The Water Management Advisory Council meets two to three times a year.

Why is my lake's water low this spring?

Water levels and flows of the lakes and rivers of the TSW fluctuate for a number of reasons. Typically, the lakes of the Trent and Severn rivers watersheds rise or refill in the spring depending upon the rate and volume of snow melt and spring rainfall.

During the winter of 2017-2018 there was a lack of significant snowfall. During our winter snow surveys, both the snow depth and moisture content were below average for almost the entire winter. Additionally, the mild spring has brought little rain to the region. The cumulative effect of both a mild winter and dry spring has resulted in less water throughout the watersheds.

You can find information about the water level of your lake or river by visiting the Water levels web site.

What is a flow through lake?

The term "flow-through" is used to describe a body of water whose levels are dependent on water flowing from an upstream lake. When flows into the lake are high, levels rise; when flows into the lake are low, levels decline.

Located between the Haliburton Lakes and the Kawartha Lakes, Shadow Lake, as an example, is a flow-through lake with no dam immediately downstream to regulate water flow out of the lake. The dam at Coboconk does not have any effect on the water level on Shadow Lake.

For more information about:

  • Water levels
  • Navigating the Trent-Severn Waterway
  • Reporting navigation hazards
  • Water level data for specific areas of the Trent-Severn Waterway
  • A dam near your property
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