Ontario gauges in the archive

1,119580 of them active

Lakes here with their own gauge

26 lakeseach named in its station

Longest inland lake record

88 yearsLake Nipissing at North Bay, 1933 to 2025

Yearly range, Lake Muskoka

0.91 mmedian at the Beaumaris gauge, 2003 to 2024

Record range, Lake Huron at Parry Sound

2.43 mon Georgian Bay, 2012 low to 1986 high

Most common highest month

Mayat 11 of 26 lake gauges

Why Lake Levels Change Through the Year

A lake rises when more water flows in than leaves it, and falls when the outflow and evaporation exceed the inflow. Each spring the freshet, the runoff from melting snow and spring rain, raises the water, and at 21 of the 26 lake gauges tabled below the median level is highest in April, May or June.

On a lake held by a dam, the year also follows an operating plan. The operator lowers the lake through the fall and winter to leave room for the spring runoff, a practice called drawdown, lets the freshet refill it, and releases water through the summer to keep the rivers below it flowing. At 20 of the 26 gauges the median level is lowest in February or March, at the end of the winter. Mindemoya Lake and Sharbot Lake are lowest in September, after the summer.

At Beaumaris on Lake Muskoka, the median May level stands 62 centimeters above the median March level. On Lake Nipissing at North Bay the median June level stands 116 centimeters above the median March level. Lake Huron at Parry Sound, on Georgian Bay, peaks later, in July, 23 centimeters above its February level.

Gauges and Datums

A water level gauge records the height of the water surface at one place, measured against a fixed mark called the gauge datum. Of the 26 lake gauges tabled here, 20 read on an assumed datum, a local mark set when the gauge was installed. A reading of 9.75 meters at Beaumaris, the high of a median year there, is a height above that mark, so readings at one gauge compare with each other exactly, and readings at two gauges on assumed datums do not compare at all. The Great Lakes gauges read on the International Great Lakes Datum of 1985, one reference for all five lakes.

Who Sets Ontario Lake Levels

The levels of the regulated systems below are set by the province, by federal bodies, by a control board and by an international commission, each under a plan of its own.

The Muskoka River System

The Ministry of Natural Resources manages water levels on the Muskoka River under the Muskoka River Water Management Plan, a plan made under Ontario’s Lakes and Rivers Improvement Act. The watershed covers about 5,100 square kilometers, from the western slopes of Algonquin Park to Georgian Bay, and holds 42 water control structures and three navigation locks. The ministry owns and operates 29 of the structures, waterpower companies eleven, the District Municipality of Muskoka one and a private owner one. Many of the dams were first built from the late 1880s to the early 1900s to move logs and power mills, and many were rebuilt in concrete between 1940 and 1970. The plan replaced the operating strategies of the Hackner-Holden Agreement of 1940, and its current version is dated December 2024.

Each lake under the plan has an annual operating plan, a band of levels for each time of year called the normal operating range, with a preferred level inside it. Dam operators hold the lake within that band under normal conditions, and in a flood or a drought the level can pass above or below it. The ministry publishes operating plans for Kawagama Lake, Lake of Bays, Mary Lake, Lake Muskoka, Lake Rosseau, Lake Joseph and Skeleton Lake, and for the Huntsville lakes, Lake Vernon, Peninsula Lake and Fairy Lake. Outside the Muskoka watershed it publishes plans for Ahmic Lake, Lake Bernard, Lake Cecebe, Doe Lake and Kahshe Lake.

The plan reduces the winter drawdown on lakes where lake trout spawn, because eggs and young fish on shallow spawning beds were exposed when levels were lowered too far. When high water is expected, those lakes are lowered further to protect the shoreline.

The Trent-Severn Waterway

Parks Canada manages water levels on the Trent-Severn Waterway, a 386-kilometer canal between Lake Ontario and Georgian Bay, and across the Trent and Severn watersheds that supply it: 60 lakes, fifteen rivers and more than 250 wetlands, with 102 operating dams. More than 35 reservoir lakes in Haliburton and northern Peterborough counties are held for the waterway.

The Haliburton and Kawartha lakes are lowered through the fall and winter to make room for the spring melt. Through the summer the reservoir lakes are drawn down, each by the same percentage, to keep navigable depths on the waterway downstream. Lake Simcoe and Lake Couchiching follow a rule curve, a guide level for each time of year, in use since 1918.

Lake Nipissing and the French River

Public Services and Procurement Canada owns and operates three dams where the French River leaves Lake Nipissing, the Big Chaudière, Portage and Little Chaudière dams, which regulate the lake’s level and the flow into the river. Through the navigation season, from the May long weekend to mid-October, the department holds the lake within an operating band.

Lake of the Woods and Lac Seul

The Lake of the Woods Control Board regulates the levels of Lake of the Woods and Lac Seul, and the flows of the Winnipeg and English rivers below them. The gauge on Pelican Lake at Sioux Lookout is one the Board contributes to the national archive.

The Great Lakes

The International Joint Commission regulates two outflows from the Great Lakes. Lake Superior’s outflow through the St. Marys River has been regulated since 1921, under Plan 2012 since 2015, and Lake Ontario’s through the St. Lawrence River since 1960, under Plan 2014. Lake Michigan and Lake Huron meet at the Straits of Mackinac and stand at one level, reported as Lake Michigan-Huron. The Commission’s Lake Superior board describes the system’s levels as shaped mainly by precipitation, runoff, evaporation and wind.

Ontario Lakes with a Water Level Gauge

Twenty-six lakes tabled here carry a Water Survey of Canada gauge named for them, with at least five years of record in the national archive. The median range between a year’s highest and lowest level runs from 0.34 m on Kenogamisis Lake to 2.35 m on Wanapitei Lake.

Nineteen of the gauges were contributed by the Ministry of Natural Resources, which in Muskoka and Parry Sound shares the cost of automatic stations on many of the larger lakes with Environment Canada. Ontario Power Generation contributed the records for Lake Nipigon, Lake Temagami and Wanapitei Lake, both discontinued. Newer gauges on Sturgeon Lake (Kawartha Lakes) at Fenelon Falls, from 2022, Lake Nipissing at West Bay, from 2023 and Lake Scugog at Scugog Island Marina, from 2022, hold fewer than five years of record and are left out of the tables.

The Record at Each Gauge

The table below states each gauge’s levels on its own datum: the high and the low of the median year, and the highest and lowest daily levels in the whole record. The figures at one gauge compare with each other, and a figure at one gauge says nothing about a figure at another.

Muskoka Water Levels

Six lakes of the Muskoka River system carry gauges of their own: Lake Muskoka at Beaumaris, Lake Rosseau at Port Carling, Lake of Bays at Baysville, Fairy Lake at Huntsville, Mary Lake at Port Sydney and Kawagama Lake at Russell Landing. All six records begin in 2003.

The ministry reads the Port Carling gauge for both Lake Rosseau and Lake Joseph, and the Huntsville gauge on Fairy Lake for the Huntsville lakes, Lake Vernon, Peninsula Lake and Fairy Lake. It publishes a conversion for each gauge that relates the gauge’s reading to the levels on the lake’s operating plan.

Lake Muskoka at Beaumaris has a median range in a year of 0.91 m, lowest in March and highest in May. The highest daily level at the gauge is 10.20 meters on its datum, on April 27, 2013, and the lowest 8.56 meters, on March 29, 2005. Of the six, Kawagama Lake has the widest range, 1.20 m in a median year, and Lake Rosseau the narrowest, 0.66 m.

Across the gauges of Muskoka and Parry Sound District, the highest levels on record at Lake Muskoka, Lake Rosseau, Lake of Bays and Kawagama Lake all fall between April 22 and April 29, 2013, and those at Fairy Lake, Mary Lake, Ahmic Lake, Lake Bernard and Doe Lake between April 24 and May 3, 2019.

Lake Nipissing Water Levels

The gauge at North Bay holds the longest record among the inland lakes tabled here: 88 years with a recorded high and low between 1933 and 2025. The median range in a year is 1.38 m, from a low in March to a high in June.

The highest daily level at North Bay is 6.93 meters on the gauge’s assumed datum, on June 23, 1947, and the lowest 4.31 meters, on April 20, 1975, a value the archive marks as estimated. A median year runs from 4.62 to 6.01 meters. The lake’s level is regulated at the French River dams, described above.

Lake Simcoe and Trent-Severn Water Levels

Parks Canada publishes the current level of Lake Simcoe, Lake Couchiching and the other Trent-Severn lakes on its water level map, from hydrometric stations it operates itself, beside the average, highest and lowest levels in records reaching back to the late 1970s or early 1980s.

No active station in the national archive carries Lake Simcoe’s name. The Water Survey of Canada gauge near Gamebridge, on the east shore, recorded the lake for 25 years between 1961 and 1994. Its median range in a year is 0.51 m, lowest in February and highest in May, and its highest daily level falls on July 3, 1967.

Gauges in the national archive on Sturgeon Lake (Kawartha Lakes) at Fenelon Falls and Lake Scugog at Scugog Island Marina began recording in 2022, and their records are still too short to summarize.

Georgian Bay Water Levels

Georgian Bay is part of Lake Huron, and its gauges carry Lake Huron’s name. Three gauges in the national archive stand on the bay: Lake Huron at Collingwood, with monthly means from 1906, Lake Huron at Parry Sound, with a record from 1963, and Lake Huron at Midland, from 2012.

At the Parry Sound gauge the median level is lowest in February and highest in July, 23 centimeters apart, and the median range between a year’s highest and lowest daily level is 0.73 m. Across the years the range is far wider. The highest daily level at Parry Sound is 177.79 meters, on November 9, 1986, and the lowest 175.36 meters, on December 20, 2012, 2.43 m apart. Both are on the International Great Lakes Datum of 1985, on which Lake Huron’s chart datum, the reference level for depths on nautical charts, is 176.00 meters.

Averaged over the twelve months of each year with a full record at Collingwood, the lowest year is 1964, at 175.70 meters, and the highest 2020, at 177.29 meters.

Great Lakes Gauges in Ontario

Where to See Today’s Water Level

The records on this page come from the national archive, which holds levels after quality checks. Each day’s level is published by the bodies below. Real-time readings are preliminary and can change before they enter the archive.

Flood Messages

Ontario’s flood messages come from the province’s Surface Water Monitoring Centre, through ministry offices and the conservation authorities. The province names four kinds: a watershed conditions statement for flood outlook, a watershed conditions statement for water safety, a flood watch and a flood warning. Current messages appear on the province’s flood message map, and low water conditions on its low water map.

Common Questions