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Acerca of

lac Brome
Physique du lac
Caractéristiques physiques

Brome Lake

20,6 km


94.6 million m3

total water

6,3 m


3,9 m3

medium discharge

12,8 m


197,28 m3

The high water mark
above the sea

10.2 months

Time to
water renewal

400 waterfront residences
300 condos


Physical characteristics

and morphological

Brome Lake is a large basin of 14.6 km2. On the east side, it is bordered by the Foster, Gauvin and Glenn mountains, from which, in particular, the Coldbrook stream starts. The lake is mainly fed by 8 tributaries which together make 278 km.


71,7 km2 



44,7 km2 



33,7 km2 



11,7 km2 



11,3 km2 



9,5 km2 



6,1 km2 


Bassin versant

The watershed

A watershed is a portion of territory delimited by ridge lines, whose waters feed a common outlet: river, lake, sea, ocean, etc. Each watershed is subdivided into a certain number of elementary basins (sometimes called "sub-watershed") corresponding to the supply surface of the tributaries flowing into the main watercourse.


The Brome Lake watershed covers an area of 186.7 km2. Increasingly, public authorities recognize that water policies must be managed according to the characteristics of each watershed. This is called watershed management.


Water flowing from a watershed crosses administrative boundaries. Thus, the Brome Lake watershed encompasses 8 municipalities, in whole or in part.  These municipalities are attached to two MRCs, namely the MRC of Brome Missisquoi and the MRC Memphrémagog. These are the municipalities of:


West Bolton


Brome Lake




Ste-Etienne de Bolton


Township of Shefford


East Bolton





Eight major tributaries

and about thirty small tributaries


The Brome Lake watershed includes 8 main tributaries and about 30 small tributaries directly to the lake. The watershed is 72.7% under forest cover. Agriculture accounts for 15.7% of the territory.

There are approximately 3,375 housing units in the watershed for a population of approximately 6,000 people. Except for approximately 2,000 housing units in Lac-Brome, all residences are under private septic systems.

carte aérienne


In 2012, a mandate to characterize and diagnose the headwater basin of Coldbrook stream was given to a team of scientists from the group of associations for the protection of the environment of lakes (RAPPEL). This project carried out in 2012 confirmed that the road network is the main cause of water degradation in this sector and that corrective measures to improve municipal infrastructure should be implemented. More than 41 sites have been identified and concrete proposals have been made to the municipal authorities.  Subsequently, three other characterization reports were produced.

CLB is convinced that this report constitutes a very good source of information for the officials of the municipalities concerned (Public Works) who will want to apply the necessary corrective measures to the quality of the water flowing into their ditches and on their roads. To view the reports, click on the links below.​​

Characterization and diagnostics
basins  slopes

Ruissellement et débits

Runoff and tributary flow

Rainwater that falls on the surface of the Brome Lake watershed infiltrates, runs off or evaporates. surface, or reach the groundwater table. In areas covered with vegetation, in a forest environment for example, the soil absorption rate is much higher than in places where the ground surface is bare of vegetation.  When the slopes are steep, there is much less infiltration, the water drops are dragged by the effect of gravity and acquire enough kinetic energy to run off on the surface. The water that is absorbed on the surface is partly used by the plants for their growth and another part evaporates. 

Land use in

the watershed

The following table shows the land use in the watershed. Our watershed is made up of 70% forest areas, these forest areas are conducive to capturing the energy of the water that falls to the ground. Tree branches and leaves absorb a certain amount of energy from the water droplets, and when they reach the ground, the surrounding vegetation picks up another part.  Even though the following table shows that only 5% of the territory covers urban regions and developed areas, because of the human activities that take place there, they have a significant contribution to the runoff and especially in the polluting loads that this water contains.

Accumulation des sédiments

Sediment accumulation


The sediments deposited in Brome Lake are formed by the deposits of suspended matter and the accumulation of other organic or inorganic substances that are present in the water.  Mineral particles are transported by the water that comes from the watershed and the organic particles come from plants and fish that die and sink to the bottom of the water.


According to Prairies, in 1997 there were 6 to 8 meters of sediment in the deepest part of the lake, and the rate of sediment accumulation would be 3 to 4 mm per year.  For a healthy lake, the sediment accumulation rate is more like .5 to 1 mm per year.  According to him, the lake supplies itself with phosphorus, as much through the phenomenon of anoxia as through organic decomposition.  

About ten years ago, RLB measured the depth of the sediments, their grain size and their phosphorus content. The following map shows the sediment depth and phosphorus concentration of the samples.

Barrage foster

Brome Lake Conservation has prepared a technical note showing the level of the lake and the water coming out of the Foster dam. We know that these two parameters are very important for the quality of the lake water, recreational activities and the drinking water supply of the town of Bromont.

However, these parameters are managed according to an agreement between the City of Lac-Brome, City of Bromont and the Government of Quebec. 

barrage foster.jpg

Foster Dam

How is the Foster Dam managed?
What are the lake levels?
Are there any changes to be made?


After analyzing this agreement and the operating datafrom 2005 to 2010, CLB found no indication that the management of thedam is generally inconsistent with the convention.

On the contrary, the management of the dam is satisfactory. Levelsof the lake are strictly managed according to the convention; the minimum flowis generally above the standard of 0.88 m3 / sec., except forspecial cases of a rise in the level of the lake in the spring orof prolonged drought at the end of the summer.

It appears that there is no need to revise in depth theconvention, if not to better reflect the operational reality andof the watershed and to do this to establish ona basemonthly minimum flow of 0.88 m3 / sec. Indeed, weestimate that the rule of 0.88 m3 / sec. "at all times" turns out, inthe state of the current devices, impractical and unnecessarily constraining.


A planning of needs over a 15-25 year horizon and the adoption of sustainable development measures to secure water supplies are suggested to the responsible authorities. For the moment, the average annual flow used by Ville de Bromont represents less than 10% of the minimum flow required by the agreement (0.066 m3 / sec. vs. 0.88 m3 / sec.).

It is clear that the challenge lies in the management of extreme events, in particular periods of drought. With this in mind, sustainable development strategies are proposed: water saving program, constitution of water reserves, use of effective management tools.


The management of

Foster dam 


The management of the Foster dam, at the outlet of Brome Lake, is currently governed by a tri-partite agreement: Government of Quebec, city of Brome Lake and  city of Bromont. The City of Brome Lake ...

The debits at

Foster dam

Hydrological monitoring of different hydrometric stations

Station: 030353   Yamaska - at the Chemin de Matapédia bridge

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