Red Horse Lake

Where Red Horse Lake is

Red Horse Lake lies in the United Counties of Leeds and Grenville, within the Township of Leeds and the Thousand Islands.

How deep is Red Horse Lake?

The deepest mapped contour on Red Horse Lake is 36.6 meters, and the water within that boundary descends even farther. Ontario’s bathymetry record holds 22 depth contours for Red Horse 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.

Red Horse Lake has 7 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 mesotrophic.

The longest record is held by site 4575/1 at W Basin-S Centre Is., with phosphorus sampled several times a year between spring and fall over 14 years to 2015. Its long-term mean phosphorus concentration is 16.7 micrograms per litre, within the mesotrophic band, which runs from 10 to 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 151 clarity readings at site 4575/1 give a median Secchi depth of 4.0 meters.

Median Secchi depth by year at site 4575/1

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

Red Horse Lake Weather

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

Red Horse Lake weather

Water temperature

No provincial monitoring station records water temperature on Red Horse Lake. The LastLake model computes the temperature of its surface water for each day from the daily mean air temperature at Environment Canada’s Grenadier Island climate station, 23 kilometers from the lake, or the next nearest station when its record is incomplete, and from the lake’s area of 296 hectares and its mean depth of 10.4 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 Red Horse Lake carries the model’s figures for the past weeks and the coming week.

See also Lake Water Temperature in Ontario

Fish in Red Horse Lake

Ontario’s aquatic resource records name 19 fish species in Red Horse Lake. The province’s other records for the lake name one further species, splake. It appears in the records below.

Popular species in the province’s records

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

Spawning areas

Ontario maps 3 fish spawning records within the Red Horse Lake outline, for two different species. One is records of under 100 square meters each, and the other two are mapped areas.

By number of records

By area mapped

• Northern Pike2 areas1.3 ha
• Lake Trout1 records100 m²

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 Red Horse Lake run from 1946 to 2015 and hold 93 releases. Lake Trout account for most of the fish: 241,733 released in 47 of the years between 1946 and 2015. The last recorded release was 5,000 lake trout yearlings in 2015.

Eating the fish

The 2026 Guide to Eating Ontario Fish carries consumption advice for four species taken from Red Horse Lake, tested for contaminants at a sampling location in Leeds & Lansdowne Twps. 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 18

Red Horse Lake lies in Fisheries Management Zone 18. Ontario sets its fishing seasons and catch limits by zone.

Fisheries management zones around Red Horse 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

Red Horse Lake Ice Fishing

An ice hut on Red Horse Lake must be removed by March 15. 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). Red Horse Lake lies within FMZ 18.

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 18 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 Red Horse 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

Red Horse Lake contains twelve islands in the Ontario Hydro Network’s outline, zero of them over 10 hectares and five under a tenth of a hectare. Four of them lie mostly inside wetland the province’s Wetland With Significance dataset maps as marsh.

Official names

Ontario’s geographic names register lists 9 official names on the water and its islands: 5 islands and three bays. A further 1 named point stands on the mainland shore.

Bays 3

• Cold Spring Bay
• Cronin Bay
• Washburn Bay

Points on the shore 1

• Long Point

Nearby lakes

• Charleston Lake5 km away
• Upper Beverley Lake9 km away
• Whitefish Lake12 km away
• Sand Lake15 km away

All lakes

Questions about Red Horse Lake

• How deep is Red Horse Lake?

  Its deepest charted contour is 36.6 meters, and the water within it is deeper.

• How big is Red Horse Lake?

  Its surface covers 3.0 square kilometers and it holds 12 islands. Of its 30 kilometers of shoreline, 28 kilometers is the mainland shore and 2 kilometers is the shore of the islands.

• What fish are in Red Horse Lake?

  Ontario’s aquatic resource records name nineteen species, among them lake trout, walleye, smallmouth bass, largemouth bass, northern pike and lake whitefish. The lake’s spawning, consumption and stocking records also name splake.

• Is the water clear?

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