Mountain Lake

Where Mountain Lake is

Mountain Lake lies in the County of Haliburton, within the Township of Minden Hills.

How deep is Mountain Lake?

The deepest mapped contour on Mountain Lake is 30.5 meters, and the water within that boundary descends even farther. Ontario’s bathymetry record holds 9 depth contours for Mountain 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.

Mountain Lake has 4 Lake Partner monitoring sites. One of them has reported phosphorus for the three or more years the province requires before a status is assigned, and is classified oligotrophic.

The longest record is held by site 3354/3 at S end, deep spot, with phosphorus sampled once a year over 24 years to 2025. Its long-term mean phosphorus concentration is 5.55 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 127 clarity readings at site 3354/3 give a median Secchi depth of 6.0 meters.

Median Secchi depth by year at site 3354/3

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

Mountain Lake Weather

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

Mountain Lake weather

Water temperature

Ontario’s aquatic resource records class Mountain Lake as a cold-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 Mountain Lake. The weather page for Mountain 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

Mountain Lake Water Level

Parks Canada measures the level of Mountain Lake at the gauge it names Mountain Lake (New), 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 Mountain Lake

Ontario’s aquatic resource records name 11 fish species in Mountain Lake. The province’s other records for the lake name one further species, smallmouth bass. It appears in the records below.

Popular species in the province’s records

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

Spawning areas

Ontario maps 4 fish spawning records within the Mountain Lake outline: 4 lake trout spawning areas covering 0.47 hectares.

By number of records

By area mapped

• Lake Trout4 areas0.5 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 Mountain Lake run from 1946 to 1991 and hold 31 releases. Lake Trout account for most of the fish: 69,740 released in 28 of the years between 1946 and 1991. The last recorded release was 4,000 lake trout yearlings in 1991.

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

Fisheries Management Zone 15

Mountain 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 Mountain Lake

Where a row reads zone-wide, the zone’s own season or limit above applies. Lake Trout: Only one line may be used when angling through the ice.

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

Mountain Lake Ice Fishing

An ice hut on Mountain 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). Mountain 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 Mountain Lake. The province’s nearest long record covers eight lakes near Dorset, about 33 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 Mountain 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

Mountain Lake contains one island in the Ontario Hydro Network’s outline, of 0.6 hectare.

Official names

Ontario’s geographic names register lists 1 official name on the water and its islands: 1 island.

Nearby lakes

• Horseshoe Lake2 km away
• Twelve Mile Lake5 km away
• Canning Lake6 km away
• South Lake8 km away

All lakes

Questions about Mountain Lake

• How deep is Mountain Lake?

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

• How big is Mountain Lake?

  Its surface covers 3.2 square kilometers and it holds 1 island. Of its 14 kilometers of shoreline, 13 kilometers is the mainland shore and 1 kilometer is the shore of the island.

• What fish are in Mountain Lake?

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

• Is the water clear?

  The one monitoring site with a phosphorus status is classified oligotrophic, the clearest of the province’s three bands.