Clear Lake

Where Clear Lake is

Clear Lake lies in the County of Peterborough, with shoreline in the Township of Selwyn and the Township of Douro-Dummer.

How deep is Clear Lake?

The deepest mapped contour on Clear Lake is 13.0 meters, and the water within that boundary descends even farther. Ontario’s bathymetry record holds 240 depth contours for Clear Lake.

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.

Clear Lake has 5 Lake Partner monitoring sites. Five 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 6955/2 at Main Basin-deep spot, sampled over 23 springs to 2025. Its long-term mean phosphorus concentration is 15.24 micrograms per litre, within the mesotrophic band, which runs from 10 to 20. The site’s 136 clarity readings give a median Secchi depth of 4.0 meters.

Water temperature

Ontario’s aquatic resource records class Clear Lake as a warm-water lake, with a mean depth of 5.8 meters against its maximum of 13.

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 Clear Lake. 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 Clear Lake 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 Clear Lake

Ontario’s aquatic resource records name 25 fish species in Clear Lake. The province classes the lake as warm water. The record took effect on 29 February 2012, and it compiles what field biologists had reported by then. The province’s other records for the lake name one further species, lake trout. It appears in the records below.

Thirteen of the 26 species in the province’s records

• Lake Whitefishtrout and whitefish
• Muskellungepike
• Walleyeperch
• Yellow Perchperch
• Smallmouth Basssunfish
• Largemouth Basssunfish
• Black Crappiesunfish
• Rock Basssunfish
• Pumpkinseedsunfish
• Bluegillsunfish
• Burbotcod
• Brown Bullheadcatfish
• Common Carpminnow

Spawning areas

Ontario maps 5 fish spawning records within the Clear Lake outline, for two species, all of them mapped areas.

By number of records

By area mapped

• Muskellunge4 areas2.9 ha
• Walleye1 area4.5 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 Clear Lake run from 1946 to 1989 and hold 64 releases. Muskellunge account for most of the fish: 917,420 released in 30 of the years between 1946 and 1989. The last recorded release was 20,000 muskellunge frys in 1989.

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

Eating the fish

The 2025 Guide to Eating Ontario Fish carries consumption advice for seven species taken from Clear Lake, tested for contaminants at a sampling location in Duoro-Dummer, & Smith Twps., Peterborough 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 17

Clear Lake lies in Fisheries Management Zone 17. Ontario sets its fishing seasons and catch limits by zone.

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. No waterbody exception names Clear Lake.

Clear Lake Ice Fishing

An ice hut on Clear Lake must be removed by March 1. Clear Lake lies in fisheries management zone 17, 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 17 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 comes and goes

No ice record is kept on Clear Lake. The province’s nearest long record covers eight lakes near Dorset, about 99 kilometers away. It holds a date for every winter since 1975, observed by eye and from cameras set on the shore.

On those eight lakes the median date of complete ice cover is December 7 and the median date of complete ice loss is April 20, a median season of 134 days.

The date the ice forms has moved later through the record: a November 26 average across 1971 to 1980, and December 11 across 2011 to 2020. The date it leaves has moved by less than a day each decade over the same period. The two charts below are drawn to one scale of 26 days, so they can be read against each other.

Ice conditions

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

Islands and names

Clear Lake contains 66 islands in the Ontario Hydro Network’s outline, two of them over 10 hectares and 36 under a tenth of a hectare. Two of them lie inside wetlands mapped in the province’s Wetland With Significance dataset.

Official names

Ontario’s geographic names register lists 25 official names on the water and its islands: 16 islands, four bays, one shoal, three rocks and one point on an island. A further 1 named point stands on the mainland shore. The register records the origin of one name: Crane Island, “A family name used for many decades.”

Bays 4

• Brysons Bay
• Cassidy Bay
• Fiddlers Bay
• Mackenzie Bay

Shoals and rocks 4

• Dry Rock
• Hannahs Rock
• Neills Shoal
• The Spoiler

Points on the shore 1

• Sandy Point

Nearby lakes

• Lovesick Lake6 km away
• Stony Lake8 km away
• Lower Buckhorn Lake9 km away
• Big Cedar Lake11 km away

All lakes

Questions about Clear Lake

• How deep is Clear Lake?

  Its deepest charted contour is 13 meters, and the water within it is deeper.

• How big is Clear Lake?

  Its surface covers 10.8 square kilometers and it holds 66 islands. Of its 48 kilometers of shoreline, 27 kilometers is the mainland shore and 21 kilometers is the shore of the islands.

• What fish are in Clear Lake?

  Ontario’s aquatic resource records name 25 species, among them walleye, smallmouth bass, largemouth bass, muskellunge, lake whitefish and yellow perch. The lake’s spawning, consumption and stocking records also name lake trout.

• Is the water clear?

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