Lake Simcoe

Where Lake Simcoe is

Lake Simcoe lies in the Regional Municipality of Durham, the Regional Municipality of York and the County of Simcoe, with shoreline in the Town of Bradford West Gwillimbury, the Township of Oro-Medonte, the Town of Innisfil, the Township of Ramara, the Town of Georgina, the Township of Brock, the City of Orillia and the City of Barrie.

How deep is Lake Simcoe?

The deepest mapped contour on Lake Simcoe is 41.0 meters, and the water within that boundary descends even farther. The chart is drawn from 2,104 depth contours recorded in Ontario’s 1957 survey.

See also Ontario's Largest and Deepest Lakes

Surveyed Depths

Ontario has surveyed the depths of several thousand of its lakes over more than half a century. Later surveys were conducted by boat with satellite positioning and produced hundreds of thousands of soundings per lake. Earlier surveys were charted by running transects across the water and drawing depth contours by hand.

Water quality

Ontario’s Lake Partner Program is a volunteer monitoring network. Participants collect water samples for phosphorus analysis and measure water clarity through the summer with a Secchi disk. Most sites are sampled for phosphorus once a year, in spring, and some several times a year between spring and fall. Phosphorus in many lakes rises through the summer, so the two kinds of average are measured on different bases.

Phosphorus is the nutrient that controls how much algae a lake can grow. A lake with little phosphorus stays clear and supports cold-water fish such as lake trout. As phosphorus rises, algae increase, the water clouds, and oxygen in the deep water falls as the algae decay. The province classifies each monitoring site by its average phosphorus:

• Oligotrophic, below 10 micrograms per litre: clear water and low algae.
• Mesotrophic, from 10 to 20: moderately productive water, with more algae and weed growth than an oligotrophic lake but rarely a bloom.
• Eutrophic, above 20: nutrient-rich water, prone to algal blooms and low oxygen at depth.

Lake Simcoe has 7 Lake Partner monitoring sites. Two have reported phosphorus for the three or more years the province requires before a status is assigned. All are classified mesotrophic.

The longest record is held by site 6982/3 at Cedarmont Beach, with phosphorus sampled several times a year between spring and fall over 23 years to 2024. Its long-term mean phosphorus concentration is 12.3 micrograms per litre, within the mesotrophic band, which runs from 10 to 20.

A Secchi disk is a white or black-and-white plate lowered on a marked line until it disappears from view. The depth at which it vanishes is the Secchi depth, a direct measure of water clarity. Clearer water gives a deeper reading.

The 169 clarity readings at site 6982/3 give a median Secchi depth of 4.0 meters.

Median Secchi depth by year at site 6982/3

See also Lake Water Quality and Blue-Green Algae in Ontario

Lake Simcoe Weather

The weather page for Lake Simcoe carries the forecast over the water, wave heights across the lake, the modelled water temperature, and the water level.

Lake Simcoe weather

Water temperature

Ontario’s aquatic resource records class Lake Simcoe as a cool-water lake, with a mean depth of 17 meters against its maximum of 41.

Lake Simcoe is one of the few lakes in Ontario with a long temperature record of its own. The Ministry of the Environment, Conservation and Parks has sampled temperature and dissolved oxygen at fixed stations on the lake since 1980, at the surface and at every meter to the bottom, about every two weeks from spring to autumn and on a few winter dates through the ice. The record holds 102,757 readings at twelve stations on the lake, eight of which were still sampled in 2024, with a further three stations on the Holland River that are left out of every figure here. Station K42 in Kempenfelt Bay, 43 meters deep, carries the longest record, 554 profiles over 45 years.

The weather page for Lake Simcoe carries the surface temperature measured at Environment Canada buoy 45151 while the buoy is on the lake, and the LastLake model’s surface water temperature for each day of the coming week.

Water temperature at a depth of one meter (twelve provincial stations on Lake Simcoe)

The stations do not read alike on one day. In April and May, when Cook’s Bay and the shallow stations warm first, the warmest and the coolest station sampled on the same day differed by about 4.2 degrees at one meter; from June to August the difference was about 3.5 degrees. Each row in the table is that station’s own record and none is a figure for the lake.

How depth changes the temperature

The chart below is the province’s record at station K42, 43 meters deep, drawn as the median temperature at each depth for each month over 45 years. In July the water at one meter is 21 degrees, at ten meters 17, at twenty meters 10, and near the bottom 7. By September the surface has cooled to 19 degrees and the water at twenty meters has warmed to 12 as the warm layer deepens. In February the water at one meter under the ice is 0.5 degrees.

Oxygen in the deep water

The same profiles record dissolved oxygen. Through the summer the deep water of Lake Simcoe is cut off from the air by the warm layer above it, and the oxygen it holds is consumed as algae settle and decay. Cold-water fish such as lake trout and lake whitefish need that deep water to hold oxygen through to autumn. The Lake Simcoe Protection Plan, in force since 2009, set a target of 7 milligrams per litre for the deep water at the end of summer.

See also Lake Water Temperature in Ontario

Lake Simcoe Water Level

Parks Canada measures the level of Lake Simcoe at a gauge on the lake, on the Trent-Severn Waterway, and posts one reading each weekday. The record below holds every reading since 1 January 2026, set against Parks Canada’s average, highest and lowest level for each day of the year.

Readings are provisional, posted by Parks Canada on weekdays, and are not intended for flood warning.

Fish in Lake Simcoe

Ontario’s aquatic resource records name 66 fish species in Lake Simcoe.

Popular species in the province’s records

• Lake Trouttrout and whitefish
• Brook Trouttrout and whitefish
• Rainbow Trouttrout and whitefish
• Brown Trouttrout and whitefish
• Lake Whitefishtrout and whitefish
• Ciscotrout and whitefish
• Chinook Salmontrout and whitefish
• Northern Pikepike
• Muskellungepike
• Walleyeperch
• Yellow Perchperch
• Smallmouth Basssunfish
• Largemouth Basssunfish
• Black Crappiesunfish
• White Crappiesunfish
• Rock Basssunfish
• Pumpkinseedsunfish
• Bluegillsunfish
• Burbotcod
• Brown Bullheadcatfish
• Channel Catfishcatfish
• Common Carpminnow

Spawning areas

Ontario maps 109 fish spawning records within the Lake Simcoe outline, for six different species. Three are records of under 100 square meters each, and the other 106 are mapped areas.

By number of records

By area mapped

• Cisco (Lake Herring)32 areas1677.2 ha
• Lake Whitefish31 areas1591.6 ha
• Lake Trout31 areas1677.2 ha
• Northern Pike10 areas1114.4 ha
• Muskellunge3 records100 m²
• Walleye1 area21.8 ha
• Walleye nursery1 area21.8 ha

The federal Fisheries Act prohibits the harmful alteration, disruption or destruction of fish habitat without an authorization, so a dock, dredging, infill or shoreline work at a mapped spawning area is reviewed on that basis.

Stocking history

Ontario’s stocking records for Lake Simcoe run from 1946 to 2015 and hold 768 releases. Lake Whitefish account for most of the fish: 22,328,649 released in 28 of the years between 1949 and 2000. The last recorded release was 1,146 muskellunge fingerlings in 2015.

Eating the fish

The 2026 Guide to Eating Ontario Fish carries consumption advice for eighteen species taken from Lake Simcoe, tested for contaminants at a sampling location in Simcoe Co., York & Durham R.M. Each figure below is the most meals a month the guide advises for a fish of that length. Where mercury sets the advice, the figure falls as the fish gets longer, because mercury accumulates over a fish’s life. A zero means the guide advises no meals of that fish at that size.

General population: adultsSensitive population: children under fifteen, women who are or may become pregnant

Fisheries Management Zone 16

Lake Simcoe lies in Fisheries Management Zone 16. Ontario sets its fishing seasons and catch limits by zone. The province describes it as a zone of large river systems, with Lake Simcoe and Lake Couchiching its large lakes, carrying important recreational and tourism fisheries under high fishing effort.

Fisheries management zones around Lake Simcoe

Where a row reads zone-wide, the zone’s own season or limit above applies.

See also Fishing Seasons in Ontario, Zone by Zone and Fish Stocking in Ontario Lakes

Lake Simcoe Ice Fishing

An ice hut on Lake Simcoe must be removed by March 15. The province sets dates for ice hut removal as a safety measure to ensure huts are removed before thawing occurs. One date applies to an entire fisheries management zone (FMZ). Lake Simcoe lies within FMZ 16.

An ice hut must also be removed before the ice breaks up, whether or not that date has passed. The deadline clears huts from the ice ahead of the thaw and does not close the fishing season.

Registration is required in FMZ 16 for an ice hut built of anything other than fabric, and for a fabric tent covering seven square meters or more. Registration is free, and the number is displayed on the outside of the hut.

Ice In / Out Date

Ice has been recorded at Kempenfelt Bay at Barrie in 172 winters since 1852, the longest of the ice records behind these pages. The median date of complete ice cover is December 28 and the median date of complete ice loss is April 18, a median season of 109 days.

The longest recorded season is 152 days in 1875-76, and the shortest is 49 days in 2023-24.

Averaged twenty winters at a time, the date of complete ice cover has moved later: December 19 in the winters from 1860, and January 8 in those from 2000. Across the same two blocks the average season has gone from 126 days to 95.

Ice in to ice out by winter at Kempenfelt Bay at Barrie

The first part of the record was assembled from reports in Barrie newspapers back to 1852, and it has been added to year by year since, most recently by Alex Mills, York University.

Ice conditions

No public record reports the thickness or the condition of the ice on Lake Simcoe on any given day. Ontario publishes ice safety guidance for anyone going out on the ice, at ontario.ca.

See also Lake Ice in Ontario and When the Lakes Will Freeze This Winter

Getting on the water

Fifty-four access marks are mapped on Lake Simcoe.

See also Boat Launches on Ontario Lakes

Islands and names

Lake Simcoe contains 31 islands in the Ontario Hydro Network’s outline, six of them over 10 hectares and thirteen under a tenth of a hectare. One of them lies mostly inside wetland the province’s Wetland With Significance dataset maps as marsh. Georgina Island, at 1,289 hectares, is larger than the next ten together, which cover 628.

Official names

Ontario’s geographic names register lists 67 official names on the water and its islands: 9 islands, twelve bays, 21 shoals, one harbour, nine points on islands and one river. A further 31 named points stand on the mainland shore. The register records the origin of one name: Burts Creek, “Local name.”

Bays 12

• Barnstable Bay
• Bradens Bay
• Carthew Bay
• Cook's Bay
• Invermara Bay
• Kempenfelt Bay
• McPhee Bay
• Shannon Bay
• Shingle Bay
• Smith's Bay
• St. Ives Bay
• Woods Bay

Shoals and rocks 21

• Bald Shoal
• Big Shoal
• Cedar Shoal
• Centre Shoal
• Cook's Bay Shoal
• Eight Mile Shoal
• Fox Island Shoal
• Hawkestone Shoal
• Jimmy Warren Shoal
• Long Shoal
• Mara Shoal
• Maynards Shoal
• McRae Shoal
• Moons Shoal
• The Ninth Shoal
• Townline Shoal
• Trout Shoal
• Whiskey Shoal
• White Shoal
• Whitefish Shoal
• Woodman Shoal

Harbours, cuts and narrows 1

• Lefroy Harbour

Points on the shore 31

• Barnfield Point
• Bear Point
• Big Bay Point
• Big Cedar Point
• Black Point
• Brechin Point
• Cedar Point
• Champlain Point
• Concord Point
• De Grassi Point
• Deep Point
• Duclos Point
• Eight Mile Point
• Ferguson Point
• Four Mile Point
• Gamebridge Point
• Invermara Point
• Jacksons Point
• Leacock Point
• Little Cedar Point
• Mara Point
• McGinnis Point
• McRae Point
• Minet's Point
• Mossington Point
• Orchard Point
• Plumb Point
• Prophet Point
• Roches Point
• Sibbald Point
• Victoria Point

Communities on the lake 20

• Barrie
• Orillia
• Keswick
• Sutton
• Jacksons Point
• Beaverton
• Atherley
• Hawkestone
• Shanty Bay
• Alcona
• Lefroy
• Pefferlaw
• Big Bay Point
• Virginia Beach
• Lagoon City
• Oro Station
• Port Bolster
• Willow Beach
• Bell Ewart
• Island Grove

Nearby lakes

• Bass Lake23 km away
• Lake Couchiching31 km away
• Lake St. John33 km away
• Canal Lake36 km away

All lakes

Questions about Lake Simcoe

• How deep is Lake Simcoe?

  Its deepest charted contour is 41 meters, and the water within it is deeper.

• How big is Lake Simcoe?

  Its surface covers 723.0 square kilometers and it holds 31 islands. Of its 303 kilometers of shoreline, 254 kilometers is the mainland shore and 49 kilometers is the shore of the islands.

• What fish are in Lake Simcoe?

  Ontario’s aquatic resource records name 66 species, among them lake trout, walleye, smallmouth bass, largemouth bass, northern pike and muskellunge.

• Is the water clear?

  All two monitoring sites with a phosphorus status are classified mesotrophic, the middle of the province’s three bands.

• Is there a public boat launch?

  Records mark nine boat launches.

• How warm is Lake Simcoe in summer?

  At the province’s stations the water at one meter has read between 19.1 and 24.1 degrees in late July and early August in most years since 1980, with a median of 22.1 in late July. The deep water stays under 10 degrees all summer.