Conditions du lac
Brome Lake
Issued : October 4, 2024
Water transparency
Water temperature
Very murky
1,1 m of visibility
17,7 °C
Medium
196,92 m
1,22 m³/sec
The attributes of the lake
Brome Lake is a large basin of 14.6 km². On the eastern side, it is bordered by the Foster, Gauvin, and Glenn mountains, from which the Coldbrook stream flows. The lake is mainly fed by 8 tributaries totaling 278 km.
20,6 km
PERIMÈTRE
94,6 M m3
VOLUME
D'EAU
6,3 m
PROFONDEUR MOYENNE
3,9 m3/sec
DÉCHARGE
MOYENNE
12,8 m
PROFONDEUR MAXIMALE
197,28 m (au dessus de la mer)
LIGNE DES
HAUTES EAUX
10,2 mois
TEMPS DE RENOUVELLEMENT
DE L'EAU
400+
RÉSIDENCES RIVERAINES
Brome Lake: the town's economic heart
It is essential to remember that the quality of the social fabric and the economic level of Lac-Brome is directly proportional to the quality of the lake water and its safe uses; the two components are intrinsically linked.
An unusable lake means, among other things, a drop in the property value of residences, loss of income for the municipality, drop in tourist attraction, the number of second homes, reduction in tourism and business customers.
Le lac vieillit...
The life of a lake on a geological scale is relatively short. Like human life, from birth, the lake ages, the walls of its basin are slowly covered with sediments from the tributaries, or organic matter that decomposes at the bottom. Slowly the lake changes, it becomes shallower, there is more siltation, aquatic plants, until the day when the lake looks more like a marsh than a body of water proper. All these changes modify the trophic level of the lake, which means: the level of biological production and the physicochemical composition of the water.
CLB measures throughout the summer the different parameters that give an indication of the trophic level of the lake. The following table shows what levels the lake is at in 2021 according to each indicator.
The mesotrophic lake
The lake is considered mesotrophic, so the lake is productive, this productivity is characterized by an increase in algae and aquatic plants. The change from an oligotrophic lake to a eutrophic lake naturally operates over a long time scale, but human activities can cause these changes to accelerate rapidly.
Abundant phosphorus and nitrogen are the main cause of this degradation.
These essential nutrients for plants, when present in excess, create an imbalance that increases the productivity of the lake. So more food, more plants and fish, but also eventually, a lack of oxygen for aerobic living beings, such as fish. The level of chlorophyll is high, which shows an environment with a very high biomass of microscopic algae in suspension. This variable places the trophic state of the lake in the eutrophic class.
As for the average concentration of dissolved organic carbon, it is 3.4 mg/l, which indicates that the water is slightly colored. The color therefore has a small effect on the transparency of the water. The loss of water transparency is therefore attributable to the algae present in the water column.
Accumulation of sediments
The sediments deposited in Brome Lake are formed by the deposition of suspended matter and the accumulation of other organic or inorganic substances present in the water. Mineral particles are carried by runoff water from the watershed and organic particles come from dead plants and fish sink to the bottom of the lake.
According to Prairies, in 1997, there were 6 to 8 meters of sediment in the deepest part of the lake, and the sediment accumulation rate was 3 to 4 mm per year. For a healthy lake, the sediment accumulation rate is closer to 0.5 to 1 mm per year. According to Prairies, the lake is self-replenishing in phosphorus, both through anoxia and organic decomposition.
About ten years ago, CLB measured the depth, grain size, and phosphorus content of the sediment. The map (left) shows sediment depth and phosphorus concentrations of the samples.
The Foster dam
The lake level and the water outflow at the lake's outlet are two very important parameters for the lake's water quality, recreational activities, and the potable water supply to downstream municipalities. Both parameters are regulated by a dam on the Yamaska River, near Route 215 South, called the Foster Dam.
In 2011, Conservation Lac Brome prepared a technical note on the management of the Foster Dam. After analyzing the tripartite agreement and operational data from 2005 to 2010, CLB found no indication that the management of the dam was generally non-compliant with the agreement. Instead, it was clarified that the challenge lies in managing extreme events, particularly periods of drought. In this context, sustainable development strategies are proposed: water conservation programs, creation of water reserves, use of efficient management tools.
