Constant Lake

Where Constant Lake is

Constant Lake lies in the County of Renfrew, within the Township of Bonnechere Valley.

How deep is Constant Lake?

The deepest mapped contour on Constant Lake is 18.3 meters, and the water within that boundary descends even farther. Ontario’s bathymetry record holds 21 depth contours for Constant 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.

No monitoring site on Constant Lake is registered with the Lake Partner Program, so no phosphorus or clarity record exists for the lake.

Water temperature

Ontario’s aquatic resource records class Constant Lake as a cold-water lake, with a mean depth of 5.1 meters against its maximum of 18.3.

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 Constant 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 Constant 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 Constant Lake

Ontario’s aquatic resource records name 14 fish species in Constant Lake. The province classes the lake as cold water. The record took effect on 15 October 2010, and it compiles what field biologists had reported by then. The province’s other records for the lake name one further species, brook trout. It appears in the records below.

Ten of the fifteen species in the province’s records

• Ciscotrout and whitefish
• Northern Pikepike
• Walleyeperch
• Yellow Perchperch
• Smallmouth Basssunfish
• Largemouth Basssunfish
• Rock Basssunfish
• Pumpkinseedsunfish
• Burbotcod
• Brown Bullheadcatfish

Stocking history

Ontario’s stocking records for Constant Lake run from 1947 to 1960 and hold 12 releases. Walleye account for most of the fish: 550,000 released in four of the years between 1947 and 1954. The last recorded release was 1,000 brook trout yearlings in 1960.

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

Eating the fish

The 2025 Guide to Eating Ontario Fish carries consumption advice for four species taken from Constant Lake, tested for contaminants at a sampling location in Grattan Twp., Renfrew 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 15

Constant Lake lies in Fisheries Management Zone 15. Ontario sets its fishing seasons and catch limits by zone. Zone 15 covers central Ontario from Georgian Bay to the Ottawa River, bounded to the north by the Pickerel River, Highway 522 and the northern edge of Algonquin Park. It takes in Parry Sound, Huntsville, Bracebridge, Bancroft, Pembroke and Renfrew, and the whole of Algonquin Provincial Park. The province describes it as a zone of many natural lake trout and brook trout lakes, with a well-developed road network and moderate angling 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. No waterbody exception names Constant Lake.

Constant Lake Ice Fishing

An ice hut on Constant Lake must be removed by March 31. Constant Lake lies in fisheries management zone 15, 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 15 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 Constant Lake. The province’s nearest long record covers eight lakes near Dorset, about 154 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 Constant Lake on any given day. Ontario publishes ice safety guidance for anyone going out on the ice, at ontario.ca.

Islands and names

Constant Lake contains 19 islands in the Ontario Hydro Network’s outline, one of them over 10 hectares and six under a tenth of a hectare. Eight of them lie inside wetlands mapped in the province’s Wetland With Significance dataset.

Official names

Ontario’s geographic names register lists 1 official name on the water and its islands: . A further 1 named point stands on the mainland shore.

Points on the shore 1

• Mohawk Place

Nearby lakes

• Lake Clear16 km away
• Black Donald Lake21 km away
• Calabogie Lake23 km away
• Lake Doré26 km away

All lakes

Questions about Constant Lake

• How deep is Constant Lake?

  Its deepest charted contour is 18.3 meters, and the water within it is deeper.

• How big is Constant Lake?

  Its surface covers 5.6 square kilometers and it holds 19 islands. Of its 44 kilometers of shoreline, 31 kilometers is the mainland shore and 13 kilometers is the shore of the islands.

• What fish are in Constant Lake?

  Ontario’s aquatic resource records name fourteen species, among them walleye, smallmouth bass, largemouth bass, northern pike and yellow perch. The lake’s spawning, consumption and stocking records also name brook trout.