Peterborough County, Ontario

Big Bald Lake

Fifty-four islands and a deepest charted contour of 9.1 meters, in the Municipality of Trent Lakes. Warm water, with fifteen species in the aquatic resource record.

Surface: 2.0 km²
Shoreline: 36 km28 mainland + 8 islands
Islands: 54
Charted depth: 9.1 m
Depth contours: 208

All figures are derived from Ontario’s survey records.

Where Big Bald Lake is

Big Bald Lake lies in the County of Peterborough, within the Municipality of Trent Lakes.

How deep is Big Bald Lake?

The deepest mapped contour on Big Bald Lake is 9.1 meters, and the water within that boundary descends even farther. Ontario’s bathymetry record holds 208 depth contours for Big Bald Lake.

The deepest charted contour on Big Bald Lake, 9.1 meters. The circle marks the centre of that contour, and the water within it is deeper. Two contours reach this depth; the largest is marked. Of the survey’s 208 contours, 94 are its own shoreline contour, one ring around the mainland and one around each island it charted, and are left off, the outline being the Ontario Hydro Network’s; the other 114 depth contours are drawn where the province published them, and along the outline where the survey placed them beyond it. Outline from the Ontario Hydro Network. Each contour is labelled with its depth in meters; zoom in where they run close.

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.

Big Bald Lake has 2 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 mesotrophic.

Lake Partner sites on Big Bald Lake with a quotable phosphorus record
Site	Location	Years	Last sampled	Classification
6941/1	Mid Lake, deep spot	22	2025	mesotrophic
6941/2	Bay nr golf course	7	2018	mesotrophic

The longest record is held by site 6941/1 at Mid Lake, deep spot, sampled over 22 springs to 2025. Its long-term mean phosphorus concentration is 11.78 micrograms per litre, within the mesotrophic band, which runs from 10 to 20. The site’s 157 clarity readings give a median Secchi depth of 3.7 meters.

Median Secchi depth by year at site 6941/1, surface at the top. The thin line through each bar spans the shallowest and deepest reading that year, and the row beneath the years gives the number of readings. Years without readings are blank.

Water temperature

Ontario’s aquatic resource records class Big Bald Lake as a warm-water lake, with a mean depth of 2.5 meters against its maximum of 9.1.

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 Big Bald 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.

Water temperature at a depth of one meter, by half-month, on eight research lakes near Dorset, 1976 to 2025. The band holds the middle 80% of the 5,240 readings taken at one meter; the line is the median. The warmest tenth of years lie above the band and the coolest tenth below it.

Satellite thermal imagery gives a surface reading on clear days: the Landsat sensors pass over Big Bald 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.

February, under ice
May
June
July
August
September
October

Temperature against depth on Harp Lake, near Dorset, as the median of every reading at that depth in that month, 1976 to 2025. Surface at the top. The thermocline is the bend in each line.

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 Big Bald Lake

Ontario’s aquatic resource records name 15 fish species in Big Bald Lake. The province classes the lake as warm water. The record took effect on 14 October 2010, and it compiles what field biologists had reported by then.

Eleven of the fifteen species in the province’s records

Muskellungepike
Walleyeperch
Yellow Perchperch
Smallmouth Basssunfish
Largemouth Basssunfish
Black Crappiesunfish
Rock Basssunfish
Pumpkinseedsunfish
Bluegillsunfish
Brown Bullheadcatfish
Common Carpminnow

The other four species in the province’s records
Family	Species
Sucker	white sucker
Minnow	golden shiner, spottail shiner
Other	lepomis sp.

Stocking history

Ontario’s stocking records for Big Bald Lake run from 1947 to 1972 and hold 48 releases. Muskellunge account for most of the fish: 602,068 released in 26 of the years between 1947 and 1972. The last recorded release was 60,000 muskellunge frys in 1972.

Fish released into Big Bald Lake, 1947 to 1972
Species	Years	Years with a release	Fish released
Muskellunge	1947 to 1972	26	602,068
Largemouth Bass	1948 to 1948	1	14

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

Fisheries Management Zone 17

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

Zone 17 seasons and limits, 2026
Species	Open season	Sport licence	Conservation licence
Atlantic Salmon	4th Sat. in Apr. to Sept 30	0	0
Brook Trout	4th Sat. in Apr. – Sept. 30	2	1
Brown Trout	4th Sat. in Apr. – Sept. 30	5	2
Channel Catfish	4th Sat. in Apr. – Nov. 15	12	6
Crappie	Open all year	30	10
Lake Trout	4th Sat. in Apr. – Sept. 30	3	1
Lake Whitefish	4th Sat. in Apr. – Nov. 15	12	6
Largemouth and Smallmouth Bass or any combination	3rd Sat. in June – Dec. 15	6	2
Muskellunge	1st Sat. in June – Dec. 15	1, must be greater than 112 cm (44 in.)	0
Northern Pike	Open all year	6	2
Pacific Salmon	4th Sat. in Apr. – Sept. 30	5	2
Rainbow Trout	4th Sat. in Apr. – Sept. 30	2	1
Sunfish	Open all year	300, only 30 may be greater than 18 cm (7.1 in.)	15
Walleye and Sauger or any combination	2nd Sat. in May – Nov. 15	4, must be between 35 – 50 cm (13.8 – 19.7 in.)	1, must be between 35 – 50 cm (13.8 – 19.7 in.)
Yellow Perch	Open all year	50	25

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 Big Bald Lake.

Big Bald Lake Ice Fishing

An ice hut on Big Bald Lake must be removed by March 1. Big Bald 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 Big Bald Lake. The province’s nearest long record covers eight lakes near Dorset, about 85 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.

Mean date of complete ice cover on eight lakes near Dorset, by decade, with the number of recorded winters beneath. Ontario Ministry of the Environment, Conservation and Parks, Dorset Environmental Science Centre.

Mean date of complete ice loss on the same eight lakes, by decade, drawn to the same scale of days as the chart above. Ontario Ministry of the Environment, Conservation and Parks, Dorset Environmental Science Centre.

Ice conditions

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

Islands and names

Big Bald Lake contains 54 islands in the Ontario Hydro Network’s outline, zero of them over 10 hectares and 35 under a tenth of a hectare. Fifteen of them lie inside wetlands mapped in the province’s Wetland With Significance dataset.

The ten largest islands outside a mapped wetland, numbered to the table. Areas are measured on the province’s outline.

The ten largest islands outside a mapped wetland
	Island	Hectares
1	unnamed	2.4
2	unnamed	0.7
3	unnamed	0.6
4	unnamed	0.4
5	unnamed	0.3
6	unnamed	0.2
7	unnamed	0.2
8	unnamed	0.2
9	unnamed	0.2
10	unnamed	0.1

Nearby lakes

Sandy Lake3 km away
Lower Buckhorn Lake8 km away
Buckhorn Lake9 km away
Lovesick Lake12 km away

All lakes

Questions about Big Bald Lake

How deep is Big Bald Lake?
Its deepest charted contour is 9.1 meters, and the water within it is deeper.
How big is Big Bald Lake?
Its surface covers 2.0 square kilometers and it holds 54 islands. Of its 36 kilometers of shoreline, 28 kilometers is the mainland shore and 8 kilometers is the shore of the islands.
What fish are in Big Bald Lake?
Ontario’s aquatic resource records name fifteen species, among them walleye, smallmouth bass, largemouth bass, muskellunge, yellow perch and black crappie.
Is the water clear?
All two monitoring sites with a phosphorus status are classified mesotrophic, the middle of the province’s three bands.

A print of Big Bald Lake

Big Bald Lake has not yet been drawn as a print. The lakes drawn so far are on the lake maps page, and a print of Big Bald Lake can be requested by email; whether it can be drawn is confirmed before any payment.

Ask about a Big Bald Lake print

Looking at a property on Big Bald Lake?

Depth and water quality are two records out of many. Our Rural & Cottage Buyer’s Report gathers what the public record holds about one specific address: shore road allowance, road access, wells, flood mapping, Crown land, wetlands and more, read and checked by a person before it is sent.

See what is in the report

What these figures do and do not say

Depth: A depth reading is the distance from the water surface on the day of survey to the lake bottom. Lake levels vary through the season and between years. The depth figure above is the deepest contour charted and is a minimum; the depth within it was not recorded. The figures for Big Bald Lake are read from the province’s bathymetry records within the Ontario Hydro Network’s outline of the lake: the deepest figure is the deepest record inside that outline, and the count is every record inside it.
Shoreline and surface: The shoreline figure is the length of the mainland shore and of every island shore added together, measured on the Ontario Hydro Network’s outline of the lake. The surface figure is the area of water inside that outline, less the area of its islands. The provincial outline is mapped to within a few meters of the shore, and a shoreline measured from a coarser map comes out shorter, which is why a figure published elsewhere is often lower.
Survey coverage: Not every survey covered every arm of a lake, and the province’s index does not always record where a survey ended.
Water quality: Each figure belongs to a single monitoring site and not to the lake as a whole. A bay receiving a creek can read differently from open water half a kilometer away. Sites are matched to Big Bald Lake by name in the province’s records.
Nearby lakes: Distances are measured between lake centres.
Islands and names: Islands are counted and measured on the Ontario Hydro Network outline; names are the register’s, placed by its own coordinate. The register names islands the outline draws as part of a larger one, and the outline holds islands the register has not named, so the two counts differ. The outline carries some lakes across marsh, so a gap in the marsh is drawn as land, and every such gap is included in the island count. Where the register has not named one and it lies mostly inside a wetland in the province’s Wetland With Significance dataset, the page names the wetland and the table of largest islands leaves it out. Wetland boundaries are mapped at their own scale and can cover a small island whole.
Depth contours: Each contour is drawn where the survey placed it, at the survey’s own positional accuracy. The survey carries its own shoreline, which differs from the Ontario Hydro Network’s outline, so a contour near the shore can run to or past the outline. Such a stretch is drawn along the outline, as a drawing convention, and is not the survey’s line there. The contour count in the stat band is the province’s, and it includes the survey’s own shoreline contour, one ring around the mainland and one around each charted island, which the map leaves off; the map’s small print gives the split.
Location: Municipal boundaries are read from the province’s records as published and can lag a boundary change.
Temperature: The temperature band is the province’s record on eight research lakes near Dorset and is a range for the half-month. It is never a reading from Big Bald Lake, and a larger and deeper lake can warm later in spring and cool later in autumn than the lakes in the record. A satellite reading measures the surface on the day of the pass. Water below the surface layer is colder than any figure on this page, and cold-water shock can occur in water below about 15 degrees.
Fish: Ontario’s fish records are compilations of existing knowledge from field biologists and do not represent exhaustive inventories. A species that is not listed was not ruled out. The species list carries one date for the whole record and none for any species.
Stocking: A stocking record is a release on a date. It says nothing about how many fish survived or about the population in the lake today.
Fishing rules: Seasons and limits are the zone’s, for the year of the dataset the page was built from, and a licence’s own conditions and any waterbody exception apply over them. The province’s regulations summary is the authority.
Ice dates: A break-up date is the day a lake was recorded as no longer completely covered by ice, and a freeze date is the day it was recorded as completely covered. Both are read from the shore. A winter carrying no date is a winter nobody recorded, and not a winter without ice. Each Dorset figure is the average of the eight lakes and is not a record of Big Bald Lake. All eight lie within 10 to 30 kilometers of Dorset. They are smaller and shallower than most of the lakes on these pages, and a smaller lake freezes sooner.
Ice hut rules: Removal dates and registration rules are set by fisheries management zone and change from time to time. The dates here were read from the province in September 2026. The province’s own fishing regulations are the authority.

Where these figures come from

Depth, shoreline, islands and named places: Ontario Ministry of Natural Resources bathymetry and the Ontario Hydro Network, © King’s Printer for Ontario, Open Government Licence – Ontario.
Phosphorus and water clarity: Ontario Lake Partner Program, Ministry of the Environment, Conservation and Parks, Open Government Licence – Ontario. Extract built 2026-08-09.
Aerial photography: Geospatial Ontario imagery, Open Government Licence – Ontario, released collections only.
Official names: Geographic Names Ontario, Ministry of Natural Resources, Open Government Licence – Ontario. Marinas: Overture Maps Foundation places data, CDLA-Permissive 2.0.
Lake outline and municipal boundaries: Ontario Hydro Network and Ontario municipal boundary records, Ministry of Natural Resources, Open Government Licence – Ontario.
Water temperature: Inland Lakes and Streams, Physical Conditions, Dorset Environmental Science Centre, Ministry of the Environment, Conservation and Parks, Open Government Licence – Ontario, 1976 to 2025. Surface temperature: Landsat 8 and 9, U.S. Geological Survey, public domain.
Fish species and thermal regime: Ontario Aquatic Resource Area records. Spawning areas: Ontario Fish Activity Area records. Both Ministry of Natural Resources, Open Government Licence – Ontario.
Stocking: Historical Fish Stocking Data and Fish Stocking Data for Recreational Purposes, Ministry of Natural Resources, Open Government Licence – Ontario.
Seasons and limits: Ontario recreational fishing regulations data, Ministry of Natural Resources, Open Government Licence – Ontario.
Fish plates: Duane Raver, U.S. Fish and Wildlife Service; U.S. Fish and Wildlife Service. All public domain.
Ice dates near Dorset: Inland Lakes and Streams, Physical Conditions, Dorset Environmental Science Centre, Ministry of the Environment, Conservation and Parks, Open Government Licence – Ontario, 1974 to 2022.
Ice hut removal dates and registration: Ontario fishing regulations, read September 2026.