Jack Lake

Where Jack Lake is

Jack Lake lies in the County of Peterborough, with shoreline in the Township of Havelock-Belmont-Methuen and the Township of North Kawartha.

How deep is Jack Lake?

Jack Lake reaches a maximum recorded depth of 54.4 meters, determined from 10,427 soundings taken during Ontario’s 2011 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.

Jack Lake 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 oligotrophic.

The longest record is held by site 2118/3 at Brook's Bay-Snake Is, with phosphorus sampled once a year over 24 years to 2025. Its long-term mean phosphorus concentration is 9.81 micrograms per litre, within the oligotrophic band, which extends to 10.

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 170 clarity readings at site 2118/3 give a median Secchi depth of 4.05 meters.

Median Secchi depth by year at site 2118/3

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

Jack Lake Weather

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

Jack Lake weather

Water temperature

Ontario’s aquatic resource records class Jack Lake as a warm-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 Jack Lake. The weather page for Jack Lake carries the LastLake model’s surface water temperature for each day of the coming week. 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.

Water temperature at a depth of one meter (eight lakes near Dorset, ON)

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.

See also Lake Water Temperature in Ontario

Jack Lake Water Level

Parks Canada measures the level of Jack Lake 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 Jack Lake

Ontario’s aquatic resource records name 19 fish species in Jack Lake.

Popular species in the province’s records

• Lake Trouttrout and whitefish
• Ciscotrout and whitefish
• Muskellungepike
• Walleyeperch
• Yellow Perchperch
• Smallmouth Basssunfish
• Largemouth Basssunfish
• Black Crappiesunfish
• Rock Basssunfish
• Pumpkinseedsunfish
• Bluegillsunfish
• Brown Bullheadcatfish

Spawning areas

Ontario maps 70 fish spawning records within the Jack Lake outline, for four different species, and all of them are mapped below.

By number of records

By area mapped

• Smallmouth Bass36 areas9.9 ha
• Muskellunge19 areas30.8 ha
• Walleye14 areas0.3 ha
• White Sucker1 area0.1 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 Jack Lake run from 1946 to 1986 and hold 81 releases. Walleye account for most of the fish: 3,795,000 released in six of the years between 1951 and 1986. The last recorded release was 1,095,000 walleye frys in 1986.

The province’s record of stocking for recreational fishing, kept from 2016, lists no release into Jack Lake.

Eating the fish

The 2026 Guide to Eating Ontario Fish carries consumption advice for nine species taken from Jack Lake, tested for contaminants at a sampling location in Burleigh & Methuen Twps., Peterborough Co. 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. Where the guide has no result yet for certain contaminants at a location, it sets a precautionary limit of 16 meals a month. 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

Jack Lake lies in Fisheries Management Zone 15. Ontario sets its fishing seasons and catch limits by zone. 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.

Fisheries management zones around Jack Lake

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

Jack Lake Ice Fishing

An ice hut on Jack Lake must be removed by March 31. 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). Jack Lake lies within FMZ 15.

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 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.

Ice In / Out Date

No ice record is kept on Jack Lake. The province’s nearest long record covers eight lakes near Dorset, about 93 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 in date (eight lakes near Dorset, ON)

Ice out date (eight lakes near Dorset, ON)

Ice conditions

No public record reports the thickness or the condition of the ice on Jack Lake 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

Four access marks are mapped on Jack Lake.

See also Boat Launches on Ontario Lakes

Islands and names

Jack Lake contains 139 islands in the Ontario Hydro Network’s outline, two of them over 10 hectares and 49 under a tenth of a hectare. Nineteen of them lie mostly inside wetland the province’s Wetland With Significance dataset maps as marsh or unclassified wetland.

Official names

Ontario’s geographic names register lists 14 official names on the water and its islands: 6 islands and seven bays.

Bays 7

• Brooks Bay
• Callahan Bay
• Long Bay
• McCoy Bay
• Rathbun Bay
• Redmond Bay
• Sharpe Bay

Nearby lakes

• Kasshabog Lake10 km away
• Chandos Lake13 km away
• Big Cedar Lake15 km away
• Anstruther Lake15 km away

All lakes

Questions about Jack Lake

• How deep is Jack Lake?

  Its maximum recorded depth is 54.4 meters, determined during Ontario’s 2011 survey.

• How big is Jack Lake?

  Its surface covers 13.5 square kilometers and it holds 139 islands. Of its 132 kilometers of shoreline, 78 kilometers is the mainland shore and 54 kilometers is the shore of the islands.

• What fish are in Jack Lake?

  Ontario’s aquatic resource records name nineteen species, among them lake trout, walleye, smallmouth bass, largemouth bass, muskellunge and yellow perch.

• Is the water clear?

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

• Is there a public boat launch?

  Records mark one boat launch.