Cassels Lake

Where Cassels Lake is

Cassels Lake lies in the District of Nipissing, within the Municipality of Temagami.

How deep is Cassels Lake?

The deepest mapped contour on Cassels Lake is 30.5 meters, and the water within that boundary descends even farther. Ontario’s bathymetry record holds 25 depth contours for Cassels 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.

Cassels Lake has 11 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 oligotrophic.

The longest record is held by site 774/8 at Deep Spot, with phosphorus sampled several times a year between spring and fall over 12 years to 2025. Its long-term mean phosphorus concentration is 6.11 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.

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

Cassels Lake Weather

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

Cassels Lake weather

Water temperature

Ontario’s aquatic resource records class Cassels Lake as a cold-water lake, with a mean depth of 9.7 meters against its maximum of 30.5.

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 Cassels Lake. The LastLake model computes the temperature of its surface water for each day from the daily mean air temperature at Environment Canada’s Earlton Climate climate station, 71 kilometers from the lake, or the next nearest station when its record is incomplete, and from the lake’s area of 741 hectares and its mean depth of 9.7 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 Cassels Lake carries the model’s figures for the past weeks and the coming week.

See also Lake Water Temperature in Ontario

Fish in Cassels Lake

Ontario’s aquatic resource records name 25 fish species in Cassels Lake.

Popular species in the province’s records

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

Spawning areas

Ontario maps 2 fish spawning records within the Cassels Lake outline: 2 walleye spawning areas covering 5.47 hectares.

By number of records

By area mapped

• Walleye2 areas5.5 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 Cassels Lake run from 1947 to 2006 and hold 38 releases. Walleye account for most of the fish: 966,915 released in seven of the years between 1947 and 2006. The last recorded release was 8,975 walleye frys in 2006.

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

Eating the fish

The 2026 Guide to Eating Ontario Fish carries consumption advice for ten species taken from Cassels Lake, tested for contaminants at a sampling location in Cassels & Riddell Twps., Nipissing 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. 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 11

Cassels Lake lies in Fisheries Management Zone 11. Ontario sets its fishing seasons and catch limits by zone.

Fisheries management zones around Cassels Lake

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

Cassels Lake Ice Fishing

An ice hut on Cassels 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). Cassels Lake lies within FMZ 11.

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 11 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 Cassels 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

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

Nearby lakes

• Net Lake6 km away
• Rabbit Lake11 km away
• Lake Temagami24 km away
• Red Cedar Lake44 km away

All lakes

Questions about Cassels Lake

• How deep is Cassels Lake?

  Its deepest charted contour is 30.5 meters, and the water within it is deeper.

• How big is Cassels Lake?

  Its surface covers 7.4 square kilometers and it holds 14 islands. Of its 51 kilometers of shoreline, 48 kilometers is the mainland shore and 3 kilometers is the shore of the islands.

• What fish are in Cassels Lake?

  Ontario’s aquatic resource records name 25 species, among them lake trout, walleye, smallmouth bass, northern pike, lake whitefish and yellow perch.

• Is the water clear?

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