Sudbury District, Ontario

Nepewassi Lake

Thirty islands and a deepest charted contour of 12.2 meters, in the municipalities of Markstay-Warren and St.-Charles east of Sudbury. Warm water, with muskellunge and northern pike spawning areas recorded.

Surface: 11.6 km²
Shoreline: 97 km81 mainland + 16 islands
Islands: 30
Charted depth: 12.2 m
Depth contours: 60

All figures are derived from Ontario’s survey records.

Where Nepewassi Lake is

Nepewassi Lake lies in the District of Sudbury, with shoreline in the Municipality of Markstay-Warren and the Municipality of St.-Charles.

How deep is Nepewassi Lake?

The deepest mapped contour on Nepewassi Lake is 12.2 meters, and the water within that boundary descends even farther. Ontario’s bathymetry record holds 60 depth contours for Nepewassi Lake.

The deepest charted contour on Nepewassi Lake, 12.2 meters. The circle marks the centre of that contour, and the water within it is deeper. Of the survey’s 60 contours, 22 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 38 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.

Nepewassi Lake has 5 Lake Partner monitoring sites. Four 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 Nepewassi Lake with a quotable phosphorus record
Site	Location	Years	Last sampled	Classification
3449/3	Mine Bay, deep spot	10	2025	mesotrophic
3449/1	NL1 – SE	9	2023	mesotrophic
3449/2	NL4 – Central	9	2023	mesotrophic
3449/4	Deepest spot, SE	3	2015	mesotrophic

The longest record is held by site 3449/3 at Mine Bay, deep spot, sampled over 10 springs to 2025. Its long-term mean phosphorus concentration is 13.21 micrograms per litre, within the mesotrophic band, which runs from 10 to 20. The site’s 50 clarity readings give a median Secchi depth of 2.0 meters.

Median Secchi depth by year at site 3449/3, 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.

Fish in Nepewassi Lake

Ontario’s aquatic resource records name 9 fish species in Nepewassi Lake. The province classes the lake as warm water. The record took effect on 18 August 2017, and it compiles what field biologists had reported by then.

Eight of the nine species in the province’s records

Northern Pikepike
Muskellungepike
Walleyeperch
Yellow Perchperch
Smallmouth Basssunfish
Rock Basssunfish
Pumpkinseedsunfish
Brown Bullheadcatfish

The other species in the province’s records
Family	Species
Sucker	white sucker

Spawning areas

Ontario maps 2 fish spawning records within the Nepewassi Lake outline, for two species, all of them mapped areas. Every record is recorded as verified and presently suitable, and none is classed as sensitive.

By number of records

By area mapped

Muskellunge1 area6.5 ha
Northern Pike1 area11.5 ha

Spawning records mapped by the province within the Nepewassi Lake outline. A record under 100 square meters is drawn as a dot; a spawning area is drawn as the outline mapped. One colour per species, the same as the bars and the list above.

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 Nepewassi Lake run from 1948 to 1972 and hold 23 releases. Walleye account for most of the fish: 2,000,000 released in seven of the years between 1948 and 1960. The last recorded release was 20,000 muskellunge frys in 1972.

Fish released into Nepewassi Lake, 1948 to 1972
Species	Years	Years with a release	Fish released
Walleye	1948 to 1960	7	2,000,000
Muskellunge	1954 to 1972	11	190,000
Smallmouth Bass	1949 to 1966	5	12,700

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

Eating the fish

The 2025 Guide to Eating Ontario Fish carries consumption advice for four species taken from Nepewassi Lake, tested for contaminants at a sampling location in Burwash, Hendrie & Hawley Twps., Sudbury Dist. 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

Walleye Mercury
Length, cm	20 to 25	25 to 30	30 to 35	35 to 40	40 to 45	45 to 50	50 to 55	55 to 60	60 to 65
General population	16	16	12	8	8	4	4	4	4
Sensitive population	8	4	4	4	0	0	0	0	0

Northern Pike Mercury
Length, cm	25 to 30	30 to 35	35 to 40	40 to 45	45 to 50	50 to 55	55 to 60	60 to 65	65 to 70	70 to 75	over 75
General population	32	16	16	16	12	12	8	8	8	8	4
Sensitive population	12	8	8	4	4	4	4	4	4	0	0

Smallmouth Bass Mercury
Length, cm	25 to 30	30 to 35	35 to 40	40 to 45
General population	16	12	8	8
Sensitive population	4	4	4	0

White Sucker Selenium
Length, cm	30 to 35	35 to 40	40 to 45
General population	32	32	16
Sensitive population	32	32	16

Fisheries Management Zone 10

Nepewassi Lake lies in Fisheries Management Zone 10. Ontario sets its fishing seasons and catch limits by zone.

Zone 10 seasons and limits, 2026
Species	Open season	Sport licence	Conservation licence
Atlantic Salmon	Jan. 1 – Sept. 30	1	0
Brook Trout	Jan. 1 – Sept. 30	5	2
Brown Trout	Open all year	5	2
Channel Catfish	Open all year	12	6
Crappie	Open all year	30	10
Lake Trout	Jan. 1 – Labour Day	2, not more than 1 greater than 40 cm (15.7 in.)	1
Lake Whitefish	Open all year	12	6
Largemouth and Smallmouth Bass or any combination	3rd Saturday in June – November 30	6	3
Muskellunge	3rd Sat. in June – Dec. 15	1, must be greater than 122 cm (48 in.)	0
Northern Pike	Open all year	6; not more than 1 greater than 61 cm, none greater than 86 cm	2; none greater than 61 cm
Pacific Salmon	Open all year	5	2
Rainbow Trout	Open all year	2	1
Splake	Open all year	5	2
Sunfish	Open all year	50	25
Walleye and Sauger or any combination	January 1 to the third Sunday in March and third Saturday in May to December 31	4, none greater than 46 cm	2, none greater than 46 cm
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 Nepewassi Lake.

Nepewassi Lake Ice Fishing

An ice hut on Nepewassi Lake must be removed by March 31. Nepewassi Lake lies in fisheries management zone 10, 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 10 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 conditions

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

Islands and names

Nepewassi Lake contains 30 islands in the Ontario Hydro Network’s outline, two of them over 10 hectares and sixteen under a tenth of a hectare.

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

The ten largest islands
	Island	Hectares
1	Salter Island	33.1
2	One Mile Island	19.4
3	Green Island	7.4
4	unnamed	6.7
5	unnamed	4.4
6	unnamed	1.8
7	unnamed	1.6
8	Nault's Island	1.4
9	unnamed	0.6
10	unnamed	0.3

Official names

Ontario’s geographic names register lists 7 official names on the water and its islands: 4 islands and three bays.

Bays 3

Barlow Bay
Mine Bay
Morel's Bay

Nearby lakes

Richard Lake22 km away
Ramsey Lake27 km away
Nepahwin Lake28 km away
Long Lake35 km away

All lakes

Questions about Nepewassi Lake

How deep is Nepewassi Lake?
Its deepest charted contour is 12.2 meters, and the water within it is deeper.
How big is Nepewassi Lake?
Its surface covers 11.6 square kilometers and it holds 30 islands. Of its 97 kilometers of shoreline, 81 kilometers is the mainland shore and 16 kilometers is the shore of the islands.
What fish are in Nepewassi Lake?
Ontario’s aquatic resource records name nine species, among them walleye, smallmouth bass, northern pike, muskellunge and yellow perch.
Is the water clear?
All four monitoring sites with a phosphorus status are classified mesotrophic, the middle of the province’s three bands.

A print of Nepewassi Lake

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

Ask about a Nepewassi Lake print

Looking at a property on Nepewassi 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 Nepewassi 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 Nepewassi 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.
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.
Spawning areas: A spawning area is drawn where the province mapped it, at the province’s stated accuracy, and the record says nothing about how many fish use it in a given year. A nest record is one nest seen on one day; a count of nests is not a count of fish, and a count of records is not a comparison between species. Whether a given piece of work needs an authorization is a determination made by Fisheries and Oceans Canada on the work itself.
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.
Eating advice: The guide’s advice is for fish taken from the lake at the tested location and applies to the size classes tested. The province’s guide is the authority and is updated each year.
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 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.
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.
Consumption advice: Guide to Eating Ontario Fish advisory database, 2025 edition, Ministry of the Environment, Conservation and Parks, 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; Timothy Knepp, U.S. Fish and Wildlife Service; U.S. Fish and Wildlife Service. All public domain.
Ice hut removal dates and registration: Ontario fishing regulations, read September 2026.