Big Rideau Lake

Where Big Rideau Lake is

Big Rideau Lake lies in the County of Lanark and the United Counties of Leeds and Grenville, with shoreline in the Township of Tay Valley, the Township of Rideau Lakes and the Township of Drummond/North Elmsley.

How deep is Big Rideau Lake?

The deepest mapped contour on Big Rideau Lake is 91.4 meters, and the water within that boundary descends even farther. The chart is drawn from 299 depth contours recorded during Ontario’s 1972 survey.

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.

Big Rideau Lake has 18 Lake Partner monitoring sites. Ten have reported phosphorus for the three or more years the province requires before a status is assigned. Six of those sites are classified oligotrophic and four mesotrophic.

The longest record is held by site 4624/4 at Tower Island-BRLA13, with phosphorus sampled once a year over 11 years to 2016. Its long-term mean phosphorus concentration is 9.03 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 18 clarity readings at site 4624/4 give a median Secchi depth of 6.5 meters.

Median Secchi depth by year at site 4624/4

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

Big Rideau Lake Weather

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

Big Rideau Lake weather

Water temperature

Ontario’s aquatic resource records class Big Rideau Lake as a cold-water lake, with a mean depth of 13.3 meters against its maximum of 91.4.

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 Big Rideau Lake. The LastLake model computes the temperature of its surface water for each day from the daily mean air temperature at Environment Canada’s Brockville Climate climate station, 40 kilometers from the lake, or the next nearest station when its record is incomplete, and from the lake’s area of 4,590 hectares and its mean depth of 13.3 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 Big Rideau Lake carries the model’s figures for the past weeks and the coming week.

See also Lake Water Temperature in Ontario

Big Rideau Lake Water Level

Parks Canada measures the level of Big Rideau Lake at a gauge on the lake, on the Rideau Canal, 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 Big Rideau Lake

Ontario’s aquatic resource records name 47 fish species in Big Rideau Lake.

Popular species in the province’s records

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

Spawning areas

Ontario maps 230 fish spawning records within the Big Rideau Lake outline, for eleven different species. Eighteen are nests or records of under 100 square meters each, and the other 212 are mapped areas.

By number of records

By area mapped

• Smallmouth Bass58 areas44.0 ha
• Lake Trout40 areas3.9 ha
• Lake Whitefish39 areas5.6 ha
• Largemouth Bass38 areas18.1 ha
• Northern Pike22 areas13.1 ha
• Yellow Perch9 areas2.0 ha
• Yellow Perch nursery4 records200 m²
• Blue Gill nursery4 records300 m²
• Emerald Shiner nursery4 records300 m²
• Walleye3 areas0.4 ha
• Pumpkinseed nursery2 nests100 m²
• Rock Bass nursery2 nests100 m²
• Northern Pike nursery2 records200 m²
• Pumpkinseed1 area0.9 ha
• Smallmouth Bass nursery1 area0.5 ha
• Largemouth Bass nursery1 area0.5 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 Big Rideau Lake run from 1930 to 2009 and hold 167 releases. Walleye account for most of the fish: 10,620,000 released in ten of the years between 1936 and 1977. The last recorded release was 11,132 lake trout yearlings in 2009.

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

Fisheries Management Zone 18

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

Fisheries management zones around Big Rideau Lake

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

Big Rideau Lake Ice Fishing

An ice hut on Big Rideau 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). Big Rideau 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 Big Rideau 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

Getting on the water

Nine access marks are mapped on Big Rideau Lake.

See also Boat Launches on Ontario Lakes

Islands and names

Big Rideau Lake contains 188 islands in the Ontario Hydro Network’s outline, four of them over 10 hectares and 80 under a tenth of a hectare. Ten of them lie mostly inside wetland the province’s Wetland With Significance dataset maps as marsh.

Official names

Ontario’s geographic names register lists 118 official names on the water and its islands: 66 islands, 24 bays, eight shoals, nine rocks, one narrows and six points on islands. A further 22 named points stand on the mainland shore.

Bays 24

• Bass Bay
• Beaver Bay
• Bellows Bay
• Bests Bay
• Briton Bay
• Coutts Bay
• Davidsons Bay
• Green Bay
• Hawse Bay
• Hoggs Bay
• Houghton Bay
• Hudson Bay
• Jacklins Bay
• MacDonalds Bay
• McLeans Bay
• McVeetys Bay
• Mill Bay
• Minnow Bay
• Murphys Bay
• Narrows Bay
• Nobles Bay
• O'Mearas Bay
• Sheldons Bay
• Sherwoods Bay

Shoals and rocks 17

• Agnes Rock
• Big Island Shoal
• Cow Island Shoal
• Cruiser Cracker
• Elswood Rock
• Gull Shoal
• Howell Rock
• Loretta Rock
• Maggie May Shoal
• Peerless Shoal
• Pumper Rock
• Rideau King Rock
• Rideau Queen Rock
• Sheep Island Shoal
• Swan Rock
• Tower Shoal
• Turtle Shoal

Harbours, cuts and narrows 1

• Rocky Narrows

Points on the shore 22

• Amis Point
• Bests Point
• Black Ance Point
• Cedar Point
• Davidsons Point
• Donovans Point
• Frost Point
• Herman Point
• Klautz Point
• MacDonalds Point
• McNamees Point
• McVeetys Point
• Murphys Point
• Pethern Point
• Pine Point
• Rams Point
• Rocky Point
• Scotch Point
• Sheldons Point
• Sherwoods Point
• Southams Point
• Tracys Point

Communities on the lake 3

• Rideau Ferry
• Freeland
• Scotch Point

Nearby lakes

• Otter Lake8 km away
• Newboro Lake17 km away
• Christie Lake18 km away
• Upper Beverley Lake20 km away

All lakes

Questions about Big Rideau Lake

• How deep is Big Rideau Lake?

  Its deepest charted contour is 91.4 meters, and the water within it is deeper.

• How big is Big Rideau Lake?

  Its surface covers 45.9 square kilometers and it holds 188 islands. Of its 228 kilometers of shoreline, 160 kilometers is the mainland shore and 68 kilometers is the shore of the islands.

• What fish are in Big Rideau Lake?

  Ontario’s aquatic resource records name 47 species, among them lake trout, walleye, smallmouth bass, largemouth bass, northern pike and muskellunge.

• Is there a public boat launch?

  Records mark three boat launches.