Blackstone Lake

Where Blackstone Lake is

Blackstone Lake lies in the District of Parry Sound, within the Township of the Archipelago.

How deep is Blackstone Lake?

The deepest mapped contour on Blackstone Lake is 57.9 meters, and the water within that boundary descends even farther. Ontario’s bathymetry record holds 23 depth contours for Blackstone 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.

Blackstone Lake has 9 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 461/1 at Mid Lake, deep spot, with phosphorus sampled once a year over 19 years to 2025. Its long-term mean phosphorus concentration is 7.68 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 113 clarity readings at site 461/1 give a median Secchi depth of 4.5 meters.

Median Secchi depth by year at site 461/1

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

Blackstone Lake Weather

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

Blackstone Lake weather

Water temperature

Ontario’s aquatic resource records class Blackstone Lake as a cold-water lake, with a mean depth of 20 meters against its maximum of 57.9.

A deep lake separates into layers through the summer. Sunlight and wind warm and mix the upper few meters, and beneath a band of rapid cooling, the thermocline, the water stays cold through the whole season. A mean depth of 20 meters places most of Blackstone Lake’s volume in that cold layer, which is the condition lake trout and lake whitefish require.

No provincial monitoring station records water temperature on Blackstone Lake. The weather page for Blackstone 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

Fish in Blackstone Lake

Ontario’s aquatic resource records name 21 fish species in Blackstone Lake.

Popular species in the province’s records

• Lake Trouttrout and whitefish
• Ciscotrout and whitefish
• Northern Pikepike
• Muskellungepike
• Walleyeperch
• Yellow Perchperch
• Smallmouth Basssunfish
• Largemouth Basssunfish
• Black Crappiesunfish
• Rock Basssunfish
• Pumpkinseedsunfish
• Burbotcod
• Brown Bullheadcatfish

Spawning areas

Ontario maps 38 fish spawning records within the Blackstone Lake outline: 38 sunfish family spawning areas covering 4.18 hectares. Every record is recorded as verified and presently suitable, and none is classed as sensitive.

By number of records

By area mapped

• Sunfish family38 areas4.2 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 Blackstone Lake run from 1946 to 2015 and hold 70 releases. Walleye account for most of the fish: 5,233,928 released in fourteen of the years between 1946 and 2006. The last recorded release was 3,000 lake trout yearlings in 2015.

Fisheries Management Zone 15

Blackstone 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 Blackstone 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

Blackstone Lake Ice Fishing

An ice hut on Blackstone 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). Blackstone 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 Blackstone Lake. The province’s nearest long record covers eight lakes near Dorset, about 74 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 Blackstone 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

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

Official names

Ontario’s geographic names register lists 8 official names on the water and its islands: 5 islands, two bays and one rock.

Bays 2

• Lawson Bay
• McRobert Bay

Shoals and rocks 1

• Black Rock

Nearby lakes

• Crane Lake4 km away
• Rankin Lake7 km away
• Otter Lake7 km away
• Clear Lake8 km away

All lakes

Questions about Blackstone Lake

• How deep is Blackstone Lake?

  Its deepest charted contour is 57.9 meters, and the water within it is deeper.

• How big is Blackstone Lake?

  Its surface covers 5.1 square kilometers and it holds 9 islands. Of its 34 kilometers of shoreline, 30 kilometers is the mainland shore and 4 kilometers is the shore of the islands.

• What fish are in Blackstone Lake?

  Ontario’s aquatic resource records name 21 species, among them lake trout, walleye, smallmouth bass, largemouth bass, northern pike and muskellunge.

• Is the water clear?

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