St. Nora Lake

Where St. Nora Lake is

St. Nora Lake lies in the County of Haliburton, within the Township of Algonquin Highlands.

How deep is St. Nora Lake?

The deepest mapped contour on St. Nora Lake is 36.6 meters, and the water within that boundary descends even farther. Ontario’s bathymetry record holds 28 depth contours for St. Nora Lake.

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 a water sample each spring for phosphorus analysis and measure water clarity through the summer with a Secchi disk.

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 spring phosphorus. Below 10 micrograms per litre is oligotrophic: clear water and low algae. From 10 to 20 is mesotrophic: moderately productive water, with more algae and weed growth than an oligotrophic lake but rarely a bloom. Above 20 is eutrophic: nutrient-rich water, prone to algal blooms and low oxygen at depth.

A Secchi disk is a 20 centimeter 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.

St. Nora Lake has 1 Lake Partner monitoring site. It 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 5146/1 at Mid Lake, deep spot, sampled over 3 springs to 2016. Its long-term mean phosphorus concentration is 4.37 micrograms per litre, within the oligotrophic band, which extends to 10.

Water temperature

Ontario’s aquatic resource records class St. Nora 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 St. Nora Lake. 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.

Satellite thermal imagery gives a surface reading on clear days: the Landsat sensors pass over St. Nora Lake every eight days at a resolution of 100 meters. In the province’s record the surface reading and the one meter reading agree to within half a degree nine times in ten in summer.

The water a few meters down is colder than any figure on this chart, in every month of the year.

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.

Fish in St. Nora Lake

Ontario’s aquatic resource records name 10 fish species in St. Nora Lake. The province classes the lake as cold water. The record took effect on 29 November 2013, and it compiles what field biologists had reported by then. The province’s other records for the lake name four further species, among them lake trout, brown bullhead and brook trout. They appear in the records below.

Eight of the fourteen species in the province’s records

• Lake Trouttrout and whitefish
• Northern Pikepike
• Yellow Perchperch
• Smallmouth Basssunfish
• Rock Basssunfish
• Pumpkinseedsunfish
• Burbotcod
• Brown Bullheadcatfish

Spawning areas

Ontario maps 5 fish spawning records within the St. Nora Lake outline: 5 lake trout spawning areas covering 0.06 hectares.

By number of records

By area mapped

• Lake Trout5 areas600 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 St. Nora Lake run from 1946 to 1991 and hold 26 releases. Lake Trout account for most of the fish: 52,970 released in 22 of the years between 1946 and 1991. The last recorded release was 2,000 lake trout yearlings in 1991.

The province’s current stocking programme, recorded from 2016, lists no release into St. Nora Lake.

Eating the fish

The 2025 Guide to Eating Ontario Fish carries consumption advice for seven species taken from St. Nora Lake, tested for contaminants at a sampling location in Stanhope & Sherborne Twps., Haliburton Co. Each figure below is the most meals a month the guide advises for a fish of that length. The advice 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 15

St. Nora Lake lies in Fisheries Management Zone 15. Ontario sets its fishing seasons and catch limits by zone. Zone 15 covers central Ontario from Georgian Bay to the Ottawa River, bounded to the north by the Pickerel River, Highway 522 and the northern edge of Algonquin Park. It takes in Parry Sound, Huntsville, Bracebridge, Bancroft, Pembroke and Renfrew, and the whole of Algonquin Provincial Park. 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.

The figures are the number of fish an angler may catch and keep in a day and have in possession, under a sport fishing licence and under a conservation licence. The rows are the whole zone’s, and they apply to every lake in it.

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.

St. Nora Lake Ice Fishing

An ice hut on St. Nora Lake must be removed by March 31. St. Nora Lake lies in fisheries management zone 15, one of the twenty zones Ontario sets its fishing rules by, and one removal date applies across the whole zone.

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 zone 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.

When the ice goes out

The ice has been recorded leaving St. Nora Lake in 21 springs between 1968 and 1990. The median date is April 25. The earliest recorded break-up is April 5 in 1981, and the latest is May 8 in 1973.

Across the 21 recorded springs the date has moved earlier by about 9.1 days each decade.

The record was contributed by Peter J. Dillon, Ontario Ministry of the Environment to the Global Lake and River Ice Phenology Database. It holds the day the ice left and carries a freeze date for only nine of those winters, too few to draw on, so it says nothing about when St. Nora Lake freezes.

Ice conditions

No public record reports the thickness or the condition of the ice on St. Nora Lake on any given day. Ontario publishes ice safety guidance for anyone going out on the ice, at ontario.ca.

Islands and names

St. Nora Lake contains two islands in the Ontario Hydro Network’s outline, of 30.8 and 0.3 hectares.

Official names

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

Nearby lakes

• Sherborne Lake4 km away
• Kushog Lake8 km away
• Big Hawk Lake8 km away
• Halls Lake9 km away

All lakes

Questions about St. Nora Lake

• How deep is St. Nora Lake?

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

• How big is St. Nora Lake?

  Its surface covers 2.7 square kilometers and it holds 2 islands. Of its 17 kilometers of shoreline, 14 kilometers is the mainland shore and 3 kilometers is the shore of the islands.

• What fish are in St. Nora Lake?

  Ontario’s aquatic resource records name ten species, among them smallmouth bass, northern pike and yellow perch. The lake’s spawning, consumption and stocking records also name lake trout, brown bullhead, brook trout and rainbow trout.

• Is the water clear?

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