Lake Simcoe ice record

173 wintersKempenfelt Bay, 1852-53 to 2024-25

Lake records tabled

26 lakesRice Lake to Red Lake, tabled below

Median ice-out near Dorset

April 20eight lakes, 1975 to 2023

Median freeze-up near Dorset

December 7eight lakes, 1975 to 2022

Freeze-up near Dorset

+3.8 dayslater each decade since 1975

Ice hut removal

Mar 1, 15, 31set by fisheries management zone

Ice-Out Dates in Ontario

Ice-out, also called break-up, is the day a lake is recorded as no longer completely covered by ice. The records tabled below cover 26 Ontario lakes, and their median dates fall between April 8 and May 10. A median is the middle date of all the recorded springs: half came earlier and half later.

The southern lakes open first. Lake Scugog and Rice Lake have a median ice-out of April 11, and Chemong Lake April 16. The Muskoka lakes follow a few days later: Lake Muskoka on April 21, Lake Rosseau on April 21, and Lake of Bays on April 23. Lake Nipissing clears on a median April 29, Lake Opeongo in Algonquin Park on April 30, and Red Lake, Kenogamisis Lake and Pelican Lake in the northwest in the second week of May.

A single lake moves by as much as six weeks from one spring to the next. The ice left Lake Muskoka as early as March 31, 1946, and as late as May 12, 1926.

Ice-Out in Muskoka and Haliburton

Lake Muskoka has a recorded ice-out in 94 springs between 1900 and 1993, with a median of April 21. Lake Rosseau has a recorded ice-out in 95 springs between 1900 and 1995 and the same median, April 21. Lake of Bays, observed at Haystack Bay, has a recorded ice-out in 81 springs between 1939 and 2019 and a median of April 23. Eight small lakes near Dorset, recorded by the province since 1975, clear on a median April 20.

In Haliburton, Head Lake (Haliburton County) at Haliburton village has a recorded ice-out in 99 springs between 1900 and 2001, with a median of April 20. Shorter records hold April 24 for Percy Lake, April 25 for Boshkung Lake, April 25 for St. Nora Lake, and April 27 for Haliburton Lake.

Ice-Out in Algonquin Park

Lake Opeongo has a recorded ice-out in 41 springs between 1964 and 2004. Its median is April 30, the earliest recorded is April 12, 1981, and the latest May 16, 1972.

Ice-Out on Lake Simcoe and Lake Couchiching

Kempenfelt Bay, the western arm of Lake Simcoe at Barrie, has a recorded ice-out for 172 springs since 1853, with a median of April 18. In 2025 the bay cleared on April 8. Lake Couchiching has a recorded ice-out in 96 springs between 1900 and 1995 and a median of April 19, and Bass Lake (Simcoe County) near Orillia a median of April 17 across twenty springs.

Ice-Out in the Kawarthas and on Rice Lake

Chemong Lake has the longest record in the region, a recorded ice-out in 110 springs between 1900 and 2017, and a median of April 16. Lake Scugog has a recorded ice-out in 93 springs between 1901 and 1995 and a median of April 11. Rice Lake, observed at Indian River, has a recorded ice-out in 34 springs between 1969 and 2002 and the same median, April 11; its earliest recorded ice-out is February 11, 1981. Gold Lake in Peterborough County has a median of April 21.

Ice-Out in Northern Ontario

Lake Nipissing has a recorded ice-out in 62 springs between 1957 and 2019, the only northern record that runs past 2000, with a median of April 29. Trout Lake (Nipissing District) at North Bay clears on a median April 28 and Ramsey Lake at Sudbury on April 27. In the northwest the ice stays into May: Red Lake on a median May 7, Kenogamisis Lake at Geraldton and Pelican Lake at Sioux Lookout both on May 9.

Ice-out guessing contests run by lake associations and community groups each set their own definition of the day, so a contest date and a recorded ice-out date can differ.

When Do Ontario Lakes Freeze?

Freeze-up, also called ice-in or ice-on, is the day a lake is recorded as completely covered by ice. Near Dorset, the median freeze-up is December 7, with the earliest recorded on November 10, 1976, and the latest on January 5, 2016.

Most long ice records hold only the day the ice left. Freeze dates are held for Kempenfelt Bay on Lake Simcoe, for eight lakes read at Environment Canada weather stations, for Boshkung Lake, and for the Dorset lakes. Among them, Kenogamisis Lake freezes first, on a median November 11, and Red Lake follows on November 22. Lake Nipissing freezes on a median December 8. Kempenfelt Bay freezes last, on a median December 28, and in 2002 the bay did not close until February 2.

How Long a Lake Stays Frozen

Median ice seasons run from 109 days on Kempenfelt Bay to 176 days on Kenogamisis Lake. Near Dorset the median season is 134 days. The longest season recorded there is 164 days, in 2018-19, and the shortest 93 days, in 2011-12.

Why Large, Deep Lakes Freeze Later

A lake freezes only after its whole body of water has cooled. Fresh water is densest at about 4 °C, so through the autumn the surface water cools, becomes heavier, sinks and is replaced from below. This mixing, called fall turnover, continues until the whole lake is near 4 °C. Water cooled below that point is lighter and stays at the surface, and ice can then form on a calm, cold night.

A deep lake holds more heat and takes longer to reach that point, and wind that keeps the surface mixed delays it further. Small, shallow lakes and sheltered bays close first, and the open water of a large lake can stay open weeks after the bays around it have frozen.

Lake Simcoe’s Ice Record, 1852 to Today

Ice on Kempenfelt Bay, at Barrie, has been recorded since the winter of 1852-53. The record spans 173 winters, with an ice-out date for 172 of them and a freeze-up date for 167, and it is the longest of the records named here and is still kept every year.

The early dates were collected from Barrie newspapers. The record was then kept year by year by Robert Sarjeant to the 1990s and by Alex Mills of York University since. The median freeze-up on the bay is December 28, the median ice-out April 18, and the median season 109 days.

Averaged twenty winters at a time, the bay’s freeze-up has moved from December 19 in the winters beginning 1860 to January 8 in those beginning 2000, and its ice-out from April 24 to April 14. Across the same two blocks the average season has gone from 126 days to 95.

The longest season on record is 152 days, in 1875-76. The shortest is 49 days, in 2023-24, when the bay froze on January 20 and cleared on March 9. The latest winter in the record, 2024-25, froze on January 10 and cleared on April 8.

Are Ontario Lakes Freezing Later?

Near Dorset, freeze-up has moved from a November 26 average in the 1970s to December 11 in the 2010s, about 3.8 days later each decade. Ice-out has moved by less than a day each decade over the same years, so the shorter season comes almost entirely off the start of winter.

The century-long ice-out records agree on the spring. Lake Rosseau and Lake Muskoka, recorded from 1900 into the 1990s, show ice-out moving by about a tenth of a day each decade. On Kempenfelt Bay, where the record runs to 2025, both ends of the season have moved: freeze-up about 1.2 days later each decade since 1852, and ice-out about 0.7 days earlier.

How Lake Ice Forms

The first ice is a thin skin on still water once the surface reaches 0 °C. After that the sheet thickens from below: heat passes up through the ice into the colder air, and water freezes onto the underside of the sheet.

Clear Ice, White Ice and Grey Ice

Clear ice is the ice that grows downward from the underside of the sheet. It forms slowly and holds little air, so the dark water shows through it, which is why it is also called black ice or blue ice.

White ice, or snow ice, forms on top of the sheet. Heavy snow presses the ice down until water rises through cracks and floods the snow, and that slush freezes. It is opaque because of the air trapped in it. Snow also insulates the ice below it and slows the growth of clear ice, so a snowy winter can build a sheet that is thick and largely white.

Grey ice is ice holding water, most often during a thaw. In spring the sheet weakens along the boundaries between its crystals into long vertical columns, a condition called candled or honeycombed ice.

Ontario’s ice safety guidance ranks clear blue ice as the strongest kind, well ahead of white or opaque ice, and calls for double the thickness on white or opaque ice. The Canadian Red Cross describes clear blue to black ice as the strongest, advises against white opaque ice, and describes grey ice, which holds water, as unsafe to stand on.

Cracks and Pressure Ridges

An ice sheet expands as it warms and contracts as it cools. On a cold night it cracks, the cracks fill with water and freeze, and the sheet is larger the next time it warms. Where two parts of a sheet push together, the ice buckles into a pressure ridge, and the ice beside a ridge is often broken or thin.

Ice in Spring: Break-Up and Ice Push

Break-up starts at the edges. Shallow water along the shore warms first, and inflowing streams open channels of water at their mouths. As the snow on the ice melts, the sheet darkens, absorbs more sunlight and candles. A weakened sheet can clear from a lake within a day or two once wind breaks it up and drives it downwind.

Ice Push and the Shoreline

Repeated through a winter, the cracking and refreezing of an ice sheet pushes its edge against the shore. This ice push can shove rocks, lift and twist docks, and damage boathouses and shoreline walls. Wind driving broken ice onto the shore at break-up, sometimes called ice shove, can do the same within hours.

Safe Ice Thickness

No public record reports the thickness or the condition of the ice on any Ontario lake on a given day. Ice thickness varies across a single lake, and the guidance on how much ice is needed for walking, skating, snowmobiles and vehicles is published by the bodies below.

Where Ice Is Often Weaker

The province’s guidance lists the places where ice is often weaker than the ice around it: over moving water and springs, near pressure cracks and old ice holes, and around the mouths of rivers and streams. It notes that ice near shore is often much thicker than ice farther out, especially early in the season, and recommends checking the thickness regularly with a spud bar (a heavy chisel on a long handle) or an auger when moving away from shore. It also notes that heavy snow on a lake slows freezing.

Ice Thickness Chart

The Canadian Red Cross publishes its 15-20-25 rule: a minimum of fifteen centimeters of ice for one person walking or skating, twenty centimeters for a group such as a skating party or a hockey game, and 25 centimeters for a snowmobile or an ATV. The Government of Ontario’s ice fishing guidance gives at least twenty centimeters of clear blue ice for a snowmobile and 30 centimeters or more for a light vehicle, and doubles both figures for white or opaque ice.

Ice Conditions Today

Georgian Bay and the Great Lakes

The Canadian Ice Service publishes daily ice charts for the Great Lakes, including Georgian Bay, through the Canadian Coast Guard’s e-Navigation portal. Each chart records the concentration and type of ice across open water, for navigation. The Great Lakes Environmental Research Laboratory in the United States publishes daily ice cover for all five lakes.

Inland Lakes, Including Lake Simcoe

No public body reports daily ice conditions on Ontario’s inland lakes. The province’s ice fishing guidance advises checking conditions with local ice hut operators and other anglers. Hut operators report on the ice at their own operations, and police services and municipalities around the larger lakes issue public warnings when ice is judged unsafe.

Snowmobile Trails

The Ontario Federation of Snowmobile Clubs publishes trail status in its Interactive Trail Guide, marking each trail available, limited or unavailable. The status reports whether a trail is open and makes no statement about the condition of the trail.

Travel on Lake Ice

Winter Roads in the Far North

Ontario’s winter roads are built each season over land, frozen rivers and lakes by remote and First Nation communities, with funding from the province. The network runs about 3,200 kilometers and connects 32 remote First Nation communities and the Town of Moosonee to the province’s highway and rail system. The roads open from around mid-January until the spring thaw.

Skating on Lake Ice

Touring on natural lake ice, known as nordic skating or wild ice skating, depends on clear ice that formed before the first heavy snow. Snow on new ice covers the smooth surface, and once flooded and refrozen it forms white ice.

Snowmobiles and Vehicles

The province’s ice fishing guidance sets separate minimum thicknesses for snowmobiles and for light vehicles, and the Federation of Snowmobile Clubs’ trail status covers crossings on its network. Ice away from the trail network has no public report.

Ice Huts and Ice Fishing in Ontario

Ontario sets no separate ice fishing season. Each species has an open season in each fisheries management zone, one of the twenty zones the province sets its fishing rules by, and those seasons apply on the ice as they do on open water.

Ice fishing requires a valid Ontario fishing licence, sport or conservation. In most waters an angler may fish through the ice with two lines, kept within 60 meters and in clear view at all times.

Ice Hut Removal Dates

Zones 9 to 12 and 14 to 20 each set a date by which ice huts must be off the ice: March 1, March 15 or March 31. Every hut must also be removed before the ice breaks up, whether or not that date has passed, and in the zones with no date the break-up rule is the only one. The removal date clears huts from the ice ahead of the thaw and does not end fishing in the zone.

Ice Hut Registration

An ice hut needs a registration number in zones 9 to 12 and 14 to 20 when it is built of anything other than fabric, or when it is a fabric tent covering 7 square meters or more once set up. Registration is free and is done once, and the same number may be used on every hut an owner has. Numbers are issued online through the Fish and Wildlife Licensing Service or in person at a participating ServiceOntario location, and no Outdoors Card is required. The number is displayed on the outside of the hut in characters at least 6.3 centimeters high.

A commercial or tourist ice fishing operation on Lake Nipissing needs a special licence, and a hut in a provincial park may need further permits from the park.

Ice Hut Dates on Selected Lakes

A lake’s zone decides its date, and neighbouring lakes can fall in different zones. Sparrow Lake and Gloucester Pool lie in zone 16, with a March 15 removal date, while most of the Muskoka lakes north of them lie in zone 15, with March 31. The province’s zone map and its Fish ON-Line viewer show which zone a lake lies in.

Where the Records Come From

Ice dates in Ontario come from people watching lakes from the shore, and three collections hold the long records.

• The Dorset lakes. Ontario’s Ministry of the Environment, Conservation and Parks records freeze-up and ice-out on eight lakes within 10 to 30 kilometers of Dorset, by eye and from cameras set on the shore, and publishes the average of the eight as one date each winter. The published record runs from 1975 to 2023.
• The Global Lake and River Ice Phenology Database, held by the National Snow and Ice Data Center in the United States, gathers ice records from observers worldwide. Its Ontario records were contributed by Peter J. Dillon of the Ontario Ministry of the Environment, by W. R. Skinner of Environment Canada, whose records were read at weather stations and airports, and by Martyn N. Futter. Most end between 1985 and 2004.
• Kempenfelt Bay. Lake Simcoe’s record is kept at York University and published on DataStream, an open platform for water data.

Some lake associations keep an ice book, a yearly note of the day the ice formed and the day it left. Published as open data, such a book becomes a public record of its lake. Two residents of Clearwater Lake near Sudbury have published their lake’s ice dates on DataStream from 2005 onward.

Common Questions