Nepahwin Lake

Where Nepahwin Lake is

Nepahwin Lake lies in the District of Sudbury, within the City of Greater Sudbury.

How deep is Nepahwin Lake?

The deepest mapped contour on Nepahwin Lake is 22.0 meters, and the water within that boundary descends even farther. Ontario’s bathymetry record holds 110 depth contours for Nepahwin Lake.

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.

Nepahwin Lake has 10 Lake Partner monitoring sites. Seven have reported phosphorus for the three or more years the province requires before a status is assigned. One of those sites is classified mesotrophic and six eutrophic.

The longest record is held by site 6053/7 at Sudbury – deep spot, NEP-1, with phosphorus sampled once a year over 11 years to 2025. Its long-term mean phosphorus concentration is 20.46 micrograms per litre, within the eutrophic band, which begins at 20.

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 1 clarity readings at site 6053/7 give a median Secchi depth of 2.5 meters.

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

Nepahwin Lake Weather

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

Nepahwin Lake weather

Water temperature

Ontario’s aquatic resource records class Nepahwin Lake as a cold-water lake, with a mean depth of 8.3 meters against its maximum of 22.

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 Nepahwin Lake. The LastLake model computes the temperature of its surface water for each day from the daily mean air temperature at Environment Canada’s Sudbury A climate station, 24 kilometers from the lake, or the next nearest station when its record is incomplete, and from the lake’s area of 127 hectares and its mean depth of 8.3 meters.

Each day’s figure carries the model’s typical error for that month on lakes of the same size. The figure in the chart below is the temperature near the surface, away from the shoreline. Bays, shallows and water deeper below the surface differ in temperature. Temperature is not measured when ice covers the lake. The weather page for Nepahwin Lake carries the model’s figures for the past weeks and the coming week.

See also Lake Water Temperature in Ontario

Fish in Nepahwin Lake

Ontario’s aquatic resource records name 13 fish species in Nepahwin Lake. The province’s other records for the lake name three further species, among them walleye and brook trout. They appear in the records below.

Popular species in the province’s records

• Lake Trouttrout and whitefish
• Rainbow Trouttrout and whitefish
• Northern Pikepike
• Walleyeperch
• Yellow Perchperch
• Smallmouth Basssunfish
• Rock Basssunfish
• Pumpkinseedsunfish
• Brown Bullheadcatfish

Stocking history

Ontario’s stocking records for Nepahwin Lake run from 1983 to 2015 and hold 26 releases. Splake account for most of the fish: 49,140 released in fourteen of the years between 1983 and 2015. The last recorded release was 3,000 splake yearlings in 2015.

Eating the fish

The 2026 Guide to Eating Ontario Fish carries consumption advice for ten species taken from Nepahwin Lake, tested for contaminants at a sampling location in McKim Twp., Sudbury Dist. 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. 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 10

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

Fisheries management zones around Nepahwin Lake

Where a row reads zone-wide, the zone’s own season or limit above applies.

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

Nepahwin Lake Ice Fishing

An ice hut on Nepahwin 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). Nepahwin Lake lies within FMZ 10.

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 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 Nepahwin 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

Islands and names

Nepahwin Lake contains seven islands in the Ontario Hydro Network’s outline, zero of them over 10 hectares and three under a tenth of a hectare.

Official names

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

Nearby lakes

• Ramsey Lake3 km away
• Richard Lake6 km away
• Long Lake14 km away
• Nepewassi Lake28 km away

All lakes

Questions about Nepahwin Lake

• How deep is Nepahwin Lake?

  Its deepest charted contour is 22 meters, and the water within it is deeper.

• How big is Nepahwin Lake?

  Its surface covers 1.3 square kilometers and it holds 7 islands. Of its 12 kilometers of shoreline, 10 kilometers is the mainland shore and 2 kilometers is the shore of the islands.

• What fish are in Nepahwin Lake?

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