Lake Couchiching

Where Lake Couchiching is

Lake Couchiching lies in the County of Simcoe, with shoreline in the Township of Severn, the Township of Oro-Medonte, the Township of Ramara and the City of Orillia.

How deep is Lake Couchiching?

Ontario’s digital bathymetry records hold no soundings and no depth contours within the Ontario Hydro Network’s outline of Lake Couchiching. Ontario’s aquatic resource record for Lake Couchiching gives a maximum depth of 12 meters and a mean depth of 6 meters.

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 a water sample each spring for phosphorus analysis and measure water clarity through the summer with a Secchi disk.

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 spring phosphorus. Below 10 micrograms per litre is oligotrophic: clear water and low algae. From 10 to 20 is mesotrophic: moderately productive water, with more algae and weed growth than an oligotrophic lake but rarely a bloom. Above 20 is eutrophic: nutrient-rich water, prone to algal blooms and low oxygen at depth.

A Secchi disk is a 20 centimeter 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.

Lake Couchiching has 4 Lake Partner monitoring sites. Four have reported phosphorus for the three or more years the province requires before a status is assigned. Three of those sites are classified oligotrophic and one mesotrophic.

The longest record is held by site 2454/3 at S end, deep spot, sampled over 13 springs to 2020. Its long-term mean phosphorus concentration is 9.39 micrograms per litre, within the oligotrophic band, which extends to 10. The site’s 53 clarity readings give a median Secchi depth of 4.5 meters.

Water temperature

Ontario’s aquatic resource records class Lake Couchiching as a cool-water lake, with a mean depth of 6 meters.

A lake separates into layers through the summer where it is deep enough. Sunlight and wind warm and mix the upper few meters, and beneath a band of rapid cooling, the thermocline, the water stays cold. A shallow lake mixes to the bottom instead and warms through, sooner in spring and later into autumn.

No provincial monitoring station records water temperature on Lake Couchiching. The province’s longest in-water record is kept on eight research lakes near Dorset, sampled since 1976. A reading is taken at the surface, at one meter, at each meter to seven and then every two meters to the bottom, about every two weeks through the open-water season and about monthly under ice. The record holds 5,240 readings at a depth of one meter.

At one meter the eight lakes track one another closely. On a day when several were sampled, the warmest and the coolest lake differed by about one degree in every month of the year, and a 12 meter deep lake and a 37 meter deep lake read within 0.2 degrees of each other from June to October. The weather of the year, and not the lake, sets most of the width of the band below.

Satellite thermal imagery gives a surface reading on clear days: the Landsat sensors pass over Lake Couchiching every eight days at a resolution of 100 meters. In the province’s record the surface reading and the one meter reading agree to within half a degree nine times in ten in summer.

The water a few meters down is colder than any figure on this chart, in every month of the year.

How depth changes the temperature

The chart below is the province’s record on Harp Lake, 37 meters deep, drawn as the median temperature at each depth for each month over 49 years. In July the water at one meter is 23 degrees, at five meters 15, at seven meters 9, and from 13 meters to the bottom under 6. By October the warm layer has deepened to seven meters and cooled to 11 degrees. In February the whole column sits between 1 and 4 degrees under the ice, coldest at the top.

A shallower lake in the same record warms sooner. Heney Lake, six meters deep, reads about 1.8 degrees warmer than Harp Lake at one meter from January to May, 0.8 degrees warmer from June to August, and the same or cooler from September.

Fish in Lake Couchiching

Ontario’s aquatic resource records name 43 fish species in Lake Couchiching. The province classes the lake as cool water. The record took effect on 29 November 2010, and it compiles what field biologists had reported by then. The province’s other records for the lake name one further species, cisco. It appears in the records below.

Seventeen of the 44 species in the province’s records

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

Spawning areas

Ontario maps 5 fish spawning records within the Lake Couchiching outline, for three species, all of them nests or records of under 100 square meters each. Every record is recorded as verified and presently suitable, and none is classed as sensitive.

By number of records

By area mapped

• Northern Pike2 records0 m²
• Muskellunge2 records0 m²
• White Sucker1 records0 m²

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 Couchiching run from 1946 to 1976 and hold 65 releases. Walleye account for most of the fish: 3,970,000 released in five of the years between 1952 and 1956. The last recorded release was 10,000 muskellunge frys in 1976.

The province’s current stocking programme, recorded from 2016, lists no release into Lake Couchiching.

Eating the fish

The 2025 Guide to Eating Ontario Fish carries consumption advice for six species taken from Lake Couchiching, tested for contaminants at a sampling location in Orillia Twp., Simcoe Co. Each figure below is the most meals a month the guide advises for a fish of that length. The advice 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 Couchiching lies in Fisheries Management Zone 16. Ontario sets its fishing seasons and catch limits by zone. Zone 16 is the most southerly inland zone in the province and takes in all of southwestern Ontario, with Toronto, Mississauga, Hamilton, Kitchener-Waterloo and London. 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.

The figures are the number of fish an angler may catch and keep in a day and have in possession, under a sport fishing licence and under a conservation licence. The rows are the whole zone’s, and they apply to every lake in it.

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

Lake Couchiching Ice Fishing

An ice hut on Lake Couchiching must be removed by March 15. Lake Couchiching lies in fisheries management zone 16, one of the twenty zones Ontario sets its fishing rules by, and one removal date applies across the whole zone.

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 zone 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.

When the ice goes out

The ice has been recorded leaving Lake Couchiching in 96 springs between 1900 and 1995. The median date is April 19. The earliest recorded break-up is March 28 in 1945, and the latest is May 5 in 1904.

Across the 96 recorded springs the median date has moved by less than a day each decade.

The record was contributed by Peter J. Dillon, Ontario Ministry of the Environment to the Global Lake and River Ice Phenology Database. It holds the day the ice left and carries no date for the day it formed, so it says nothing about when Lake Couchiching freezes.

Ice conditions

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

Islands and names

Lake Couchiching contains 44 islands in the Ontario Hydro Network’s outline, two of them over 10 hectares and 26 under a tenth of a hectare. Two of them lie inside wetlands mapped in the province’s Wetland With Significance dataset. Chiefs Island, at 61 hectares, is larger than the next ten together, which cover 30.

Official names

Ontario’s geographic names register lists 20 official names on the water and its islands: 10 islands, seven bays, one shoal and one narrows. A further 7 named points stand on the mainland shore. The register records the origin of one name: Dougall Canal, “Name is in honour of the individual who designed, constructed and financed the construction of the canal in 1960-1967.”

Bays 7

• Cunningham Bay
• Grays Bay
• Hopkins Bay
• Old Brewery Bay
• Pumpkin Bay
• Quarry Bay
• Woods Bay

Shoals and rocks 1

• The Limestones

Harbours, cuts and narrows 1

• The Narrows

Points on the shore 7

• Barnfield Point
• Couchiching Point
• Floral Point
• Heward Point
• Invermara Point
• Leacock Point
• Owaissa Point

Nearby lakes

• Bass Lake13 km away
• Sparrow Lake16 km away
• Dalrymple Lake20 km away
• Kahshe Lake21 km away

All lakes

Questions about Lake Couchiching

• How big is Lake Couchiching?

  Its surface covers 45.4 square kilometers and it holds 44 islands. Of its 79 kilometers of shoreline, 61 kilometers is the mainland shore and 18 kilometers is the shore of the islands.

• What fish are in Lake Couchiching?

  Ontario’s aquatic resource records name 43 species, among them lake trout, walleye, smallmouth bass, largemouth bass, northern pike and muskellunge. The lake’s spawning, consumption and stocking records also name cisco.