Sydenham Lake

Where Sydenham Lake is

Sydenham Lake lies in the County of Frontenac, within the Township of South Frontenac.

How deep is Sydenham Lake?

The deepest mapped contour on Sydenham Lake is 33.5 meters, and the water within that boundary descends even farther. Ontario’s bathymetry record holds 15 depth contours for Sydenham 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.

Sydenham Lake has 3 Lake Partner monitoring sites. Three have reported phosphorus for the three or more years the province requires before a status is assigned. All are classified mesotrophic.

The longest record is held by site 5284/1 at Eel Bay, deep spot, with phosphorus sampled several times a year between spring and fall over 11 years to 2025. Its long-term mean phosphorus concentration is 12.44 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 19 clarity readings at site 5284/1 give a median Secchi depth of 4.0 meters.

Median Secchi depth by year at site 5284/1

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

Sydenham Lake Weather

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

Sydenham Lake weather

Water temperature

No provincial monitoring station records water temperature on Sydenham Lake. The LastLake model computes the temperature of its surface water for each day from the daily mean air temperature at Environment Canada’s Kingston Climate climate station, 24 kilometers from the lake, or the next nearest station when its record is incomplete, and from the lake’s area of 660 hectares and its mean depth. The province’s records give no mean depth for Sydenham Lake; the model uses 7.8 meters, estimated from the lake’s depth contours.

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 Sydenham Lake carries the model’s figures for the past weeks and the coming week.

See also Lake Water Temperature in Ontario

Fish in Sydenham Lake

Ontario’s aquatic resource records name 20 fish species in Sydenham Lake. The province’s other records for the lake name two further species, muskellunge and lake trout. They appear in the records below.

Popular species in the province’s records

• Ciscotrout and whitefish
• Northern Pikepike
• Yellow Perchperch
• Smallmouth Basssunfish
• Largemouth Basssunfish
• Black Crappiesunfish
• Rock Basssunfish
• Pumpkinseedsunfish
• Bluegillsunfish
• Brown Bullheadcatfish

Spawning areas

Ontario maps 7 fish spawning records within the Sydenham Lake outline, for three different species, and all of them are mapped below.

By number of records

By area mapped

• Sunfish family5 areas0.4 ha
• Smallmouth Bass1 area0.2 ha
• Largemouth Bass1 area800 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 Sydenham Lake run from 1946 to 1967 and hold 20 releases. Muskellunge account for most of the fish: 240,700 released in five of the years between 1958 and 1967. The last recorded release was 20,000 muskellunge frys in 1967.

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

Eating the fish

The 2026 Guide to Eating Ontario Fish carries consumption advice for four species taken from Sydenham Lake, tested for contaminants at a sampling location in Loughborough Twp., Frontenac Co. 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 18

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

Fisheries management zones around Sydenham Lake

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

Sydenham Lake Ice Fishing

An ice hut on Sydenham 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). Sydenham 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 Sydenham 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

Sydenham Lake contains 68 islands in the Ontario Hydro Network’s outline, zero of them over 10 hectares and 38 under a tenth of a hectare. Twenty-eight of them lie mostly inside wetland the province’s Wetland With Significance dataset maps as marsh or open water. The largest two, of 2.0 and 1.4 hectares, fall inside the Eel's Bay wetland.

Official names

Ontario’s geographic names register lists 2 official names on the water and its islands: 1 island and one bay.

Bays 1

• Eel Bay

Nearby lakes

• Loughborough Lake11 km away
• Desert Lake13 km away
• Dog Lake15 km away
• Devil Lake18 km away

All lakes

Questions about Sydenham Lake

• How deep is Sydenham Lake?

  Its deepest charted contour is 33.5 meters, and the water within it is deeper.

• How big is Sydenham Lake?

  Its surface covers 6.6 square kilometers and it holds 68 islands. Of its 56 kilometers of shoreline, 35 kilometers is the mainland shore and 21 kilometers is the shore of the islands.

• What fish are in Sydenham Lake?

  Ontario’s aquatic resource records name twenty species, among them smallmouth bass, largemouth bass, northern pike, yellow perch and black crappie. The lake’s spawning, consumption and stocking records also name muskellunge and lake trout.

• Is the water clear?

  All three monitoring sites with a phosphorus status are classified mesotrophic, the middle of the province’s three bands.