Weslemkoon Lake

Where Weslemkoon Lake is

Weslemkoon Lake lies in the County of Lennox and Addington and the County of Hastings, with shoreline in the Township of Tudor and Cashel and the Township of Addington Highlands.

How deep is Weslemkoon Lake?

The deepest mapped contour on Weslemkoon Lake is 51.8 meters, and the water within that boundary descends even farther. Ontario’s bathymetry record holds 74 depth contours for Weslemkoon 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.

Weslemkoon Lake has 13 Lake Partner monitoring sites. Seven have reported phosphorus for the three or more years the province requires before a status is assigned. All are classified oligotrophic.

The longest record is held by site 5795/4 at Main Basin-deep spot, sampled over 4 springs to 2008. Its long-term mean phosphorus concentration is 6.12 micrograms per litre, within the oligotrophic band, which extends to 10. The site’s 3 clarity readings give a median Secchi depth of 5.0 meters.

Water temperature

Ontario’s aquatic resource records class Weslemkoon Lake as a cold-water lake.

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 Weslemkoon 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 Weslemkoon 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 Weslemkoon Lake

Ontario’s aquatic resource records name 13 fish species in Weslemkoon Lake. The province classes the lake as cold water. The record took effect on 25 May 2018, and it compiles what field biologists had reported by then. The province’s other records for the lake name two further species, cisco and rainbow trout. They appear in the records below.

Eight of the fifteen species in the province’s records

• Lake Trouttrout and whitefish
• Brook Trouttrout and whitefish
• Yellow Perchperch
• Smallmouth Basssunfish
• Largemouth Basssunfish
• Rock Basssunfish
• Pumpkinseedsunfish
• Brown Bullheadcatfish

Spawning areas

Ontario maps 7 fish spawning records within the Weslemkoon Lake outline: 7 lake trout spawning areas covering 0.28 hectares.

By number of records

By area mapped

• Lake Trout7 areas0.3 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 Weslemkoon Lake run from 1946 to 1994 and hold 64 releases. Lake Herring account for most of the fish: 350,000 released in one of the years between 1952 and 1952. The last recorded release was 8,500 lake trout yearlings in 1994.

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

Eating the fish

The 2025 Guide to Eating Ontario Fish carries consumption advice for five species taken from Weslemkoon Lake, tested for contaminants at a sampling location in Ashby & Effingham Twps., Lennox & Addington Cos. 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 18

Weslemkoon Lake lies in Fisheries Management Zone 18. 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 Weslemkoon Lake.

Weslemkoon Lake Ice Fishing

An ice hut on Weslemkoon Lake must be removed by March 15. Weslemkoon Lake lies in fisheries management zone 18, 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 18 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 Weslemkoon Lake. The province’s nearest long record covers eight lakes near Dorset, about 120 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 Weslemkoon Lake on any given day. Ontario publishes ice safety guidance for anyone going out on the ice, at ontario.ca.

Islands and names

Weslemkoon Lake contains 154 islands in the Ontario Hydro Network’s outline, seven of them over 10 hectares and 62 under a tenth of a hectare. Twenty-two of them lie inside wetlands mapped in the province’s Wetland With Significance dataset.

Official names

Ontario’s geographic names register lists 50 official names on the water and its islands: 47 islands and one bay. A further 1 named point stands on the mainland shore. The register records the origin of 33 names.

Bays 1

• West Bay

Points on the shore 1

• Kegona Point

Nearby lakes

• Skootamatta Lake25 km away
• Buckshot Lake29 km away
• Centennial Lake33 km away
• Kashwakamak Lake37 km away

All lakes

Questions about Weslemkoon Lake

• How deep is Weslemkoon Lake?

  Its deepest charted contour is 51.8 meters, and the water within it is deeper.

• How big is Weslemkoon Lake?

  Its surface covers 19.7 square kilometers and it holds 154 islands. Of its 167 kilometers of shoreline, 99 kilometers is the mainland shore and 68 kilometers is the shore of the islands.

• What fish are in Weslemkoon Lake?

  Ontario’s aquatic resource records name thirteen species, among them lake trout, smallmouth bass, largemouth bass, yellow perch and brook trout. The lake’s spawning, consumption and stocking records also name cisco and rainbow trout.

• Is the water clear?

  All seven monitoring sites with a phosphorus status are classified oligotrophic, the clearest of the province’s three bands.