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Lake Memphremagog

Lake on the border of Vermont and Quebec

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  • 8 chapters

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Physical characteristics

The lake is 31 miles (50 km) long with 73 percent of the lake's surface area in Quebec, where it drains into the Magog River. However, three-quarters of its watershed, 489 square miles (1,270 km2), is in Vermont. The total is 687 square miles (1,780 km2), with 198 square miles (510 km2) located in Quebec. In Vermont, the lake lies in parts of the towns of Derby and Newport, in addition to the City of Newport, all in Orleans County. In Quebec, the lake lies in parts of Austin, Magog, Ogden, Potton, Saint-Benoît-du-Lac, and Stanstead Township, all in Memphrémagog Regional County Municipality. The lake occupies most of what the Vermont Agency of Natural Resources calls "Basin 17". At the very south end of the lake, there is the South Bay, connected by the narrowest part of the lake.

The lake elevation is approximately 682 feet (208 m) above mean sea level. The lake level is set in the treaty signed in 1935 between the United States and Canada and is controlled by the dam on the Magog River at the northern end of the lake. Both ends of the lake are fairly shallow, with depth ranges of 20 feet (6.1 m) to 30 feet (9.1 m). The lake bottom takes a dramatic drop in Canada, starting opposite Mont Owl's Head and continuing that way north to Gibraltar Point, where it starts to climb back to the shallows of the north end. Its maximum recorded depth of 351 feet (107 m) is located in Canada, opposite Jewett Point (at approximately 45°06′42″N 72°16′43″W / 45.111621°N 72.278491°W). The lake is the third deepest in Vermont. It contains 21 islands. Province Island, the largest, is divided by the international border. The lake is irregular in shape, and along its shores are several striking indentations, in some places low, and in some other parts high and rocky. Along the western shore of the lake are several mountains, prominent among which are Owl's Head, Elephantis, and the Hog's Back.

Islands

There are 21 islands on Lake Memphremagog. Of these, five are in the United States, one is international, and 15 are in Canada. Many of the islands have had several names throughout history; the current names are provided.

Islands in the United States

  • Horseneck Island (at approximately 44°57′53″N 72°12′10″W / 44.964724°N 72.202708°W) is the southernmost island on the lake and is near the eastern shore.
  • Bell Island (at approximately 44°59′28″N 72°12′34″W / 44.991006°N 72.209435°W) is one of the Twin Sister islands (the other being Black Island) and is south of Gull Rocks and Black Island.
  • Gull Rocks (at approximately 44°59′35″N 72°12′48″W / 44.993100°N 72.213430°W) is north of Bell Island and south of Black Island.
  • Black Island (at approximately 44°59′45″N 72°12′35″W / 44.995945°N 72.209696°W) is one of the Twin Sister islands (the other being Bell Island) and is north of Gull Rocks and Bell Island.
  • Cove Island (at approximately 44°59′48″N 72°12′15″W / 44.996791°N 72.204096°W) is east of Black Island.

International Islands

  • Province Island (at approximately 45°00′31″N 72°13′57″W / 45.008640°N 72.232398°W) is crossed by the international boundary. About one tenth of the southern end of the island is in the United States; the remainder is in Canada.

Islands in Canada

  • Tea Table Island (at approximately 45°00′53″N 72°13′16″W / 45.014670°N 72.221026°W) is north-northeast of Province Island, west of Reid Bay, and south of the Cedarville Wharf.
  • Round Island (at approximately 45°02′42″N 72°16′15″W / 45.044951°N 72.270706°W) is near the western shore of the lake.
  • Whetstone Island (at approximately 45°03′11″N 72°14′09″W / 45.053054°N 72.235773°W) is on the eastern shore at the entrance to Fitch Bay and is south of Gull Island. It is named for the novaculite oil stone (sold as "Magog Oil Stone") that was mined there.
  • Gull Island (at approximately 45°03′31″N 72°14′01″W / 45.058500°N 72.233473°W) is north of Whetstone Island and at the entrance to Fitch Bay.
  • Loon Island (at approximately 45°04′37″N 72°13′10″W / 45.076915°N 72.219525°W) is in Fitch Bay.
  • Minnow Island (at approximately 45°03′32″N 72°15′51″W / 45.058754°N 72.264065°W) is east of Skinner's island. The island is primarily composed of granite.
  • Skinner's Island (at approximately 45°03′33″N 72°16′00″W / 45.059246°N 72.266790°W) is west of Minnow Island and south of Long Island.The island is primarily composed of granite.
  • Long Island (at approximately 45°03′56″N 72°16′08″W / 45.065680°N 72.268839°W) is north of Skinner's Island.
  • Molson's Island (at approximately 45°05′44″N 72°16′15″W / 45.095514°N 72.270728°W) is on the eastern shore.
  • Lord's Island (at approximately 45°10′26″N 72°14′19″W / 45.173796°N 72.238638°W).
  • Eagle Island (at approximately 45°14′10″N 72°11′05″W / 45.236088°N 72.184592°W) is north of Hermitage Point and west of Hermitage Bay.
  • Three Sisters (at approximately 45°14′42″N 72°10′42″W / 45.245123°N 72.178455°W, 45°14′45″N 72°10′41″W / 45.245822°N 72.177972°W, and 45°14′52″N 72°10′36″W / 45.247726°N 72.176727°W) are three small islands that are grouped together.
  • Charest Island (at approximately 45°15′48″N 72°09′39″W / 45.263381°N 72.160739°W) is the northernmost island on the lake and is in Magog, Quebec.

Hydrology

Four Vermont rivers directly empty into the lake: the Clyde, Barton, the Black and the Johns River.

In the middle of the winter, the ice on the lake can become 3 feet (0.9 m) thick.

The Magog River, in Quebec, drains the lake towards the northeast. The hydroelectric-producing Memphemagog Dam, on the Magog River, regulates the water level of the lake. Its level is governed by a treaty signed in 1935 between the United States and Canada.

Geology

During the ice age, the lake was a proglacial lake which covered Lake Magog, Lake Brompton, and much of the Saint François watershed including East Angus, Sherbrooke, and Windsor.

Ecology

Like many other lakes, Memphremagog is accumulating phosphorus, sediments, and other pollutants, primarily runoff from farms, but from other sources as well. Exotic species infestations are a concern, with an existing Eurasian water milfoil population and the potential for a zebra mussel infestation. Since the 1970s, significant efforts have been made to reduce the polluting effects of direct discharges into the lake and its tributaries, and lake quality has improved.

In 1994, the Lake Memphremagog Watershed Association was formed to focus on solving lake and river issues. Testing done in 2008 was unable to determine the cause of excessive nitrogen and phosphorus. In 2010, a study revealed that farms contribute disproportionately to nutrient loads. Although farms have 16% of total land use in the drainage area, they produce 44% of the runoff. Baseline nutrients for a lake are 14 micrograms of phosphorus per litre of water. The lake was measured at 17 micrograms, 18% above the standard. Although the acreage devoted to farming has decreased, the retired land has most often been developed, itself a source of runoff.

In 2026, a clonally transmissible melanoma was identified among brown bullhead catfish in the lake.

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