Otter Lake

Where Otter Lake is

Otter Lake lies in the District of Parry Sound, within the Township of Seguin.

How deep is Otter Lake?

Otter Lake reaches a maximum recorded depth of 45.3 meters, determined from 4,978 soundings taken during Ontario’s 2013 survey.

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.

Otter Lake Aerial Photography

Ontario photographs the province from the air on a rolling schedule.

The photograph below is from the SCOOP2023 collection, flown in 2023 and 2024.

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.

Otter Lake has 9 Lake Partner monitoring sites. Six have reported phosphorus for the three or more years the province requires before a status is assigned. All are classified oligotrophic.

The longest record is held by site 4193/1 at OT01, sampled over 16 springs to 2018. Its long-term mean phosphorus concentration is 5.79 micrograms per litre, within the oligotrophic band, which extends to 10. The site’s 128 clarity readings give a median Secchi depth of 5.9 meters.

Water temperature

Ontario’s aquatic resource records class Otter Lake as a cold-water lake, with a mean depth of 11 meters against its maximum of 45.3.

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 Otter 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 Otter 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 Otter Lake

Ontario’s aquatic resource records name 12 fish species in Otter Lake. The province classes the lake as cold water. The record took effect on 14 December 2016, and it compiles what field biologists had reported by then. The province’s other records for the lake name two further species, rainbow trout and brook trout. They appear in the records below.

Ten of the fourteen species in the province’s records

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

Spawning areas

Ontario maps 81 fish spawning records within the Otter Lake outline, for two species, all of them mapped areas.

By number of records

By area mapped

• Sunfish family53 areas10.8 ha
• Lake Trout28 areas1.0 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 Otter Lake run from 1946 to 2001 and hold 30 releases. Lake Trout account for most of the fish: 49,698 released in 21 of the years between 1946 and 1998. The last recorded release was 4,000 rainbow trout fingerlings in 2001.

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

Eating the fish

The 2025 Guide to Eating Ontario Fish carries consumption advice for six species taken from Otter Lake, tested for contaminants at a sampling location in Foley Twp., Parry Sound Dist. 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

Otter 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.

Otter Lake Ice Fishing

An ice hut on Otter Lake must be removed by March 31. Otter 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 comes and goes

No ice record is kept on Otter Lake. The province’s nearest long record covers eight lakes near Dorset, about 79 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 conditions

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

Getting on the water

Six access marks are mapped on Otter Lake: three boat launches, one shoreline access point, one marina and one beach. Four are Ontario’s own records and two are from the Overture Places dataset, and the list under the map says which is which. Boat launch is the province’s class for a ramp; shoreline access is its class for a place the public can reach the water on foot.

Islands and names

Otter Lake contains 13 islands in the Ontario Hydro Network’s outline, zero of them over 10 hectares and four under a tenth of a hectare.

Official names

Ontario’s geographic names register lists 8 official names on the water and its islands: 6 islands and one narrows.

Harbours, cuts and narrows 1

• Otter Lake Narrows

Nearby lakes

• Blackstone Lake7 km away
• Crane Lake8 km away
• Horseshoe Lake8 km away
• Whitefish Lake13 km away

All lakes

Questions about Otter Lake

• How deep is Otter Lake?

  Its maximum recorded depth is 45.3 meters, determined during Ontario’s 2013 survey.

• How big is Otter Lake?

  Its surface covers 5.6 square kilometers and it holds 13 islands. Of its 57 kilometers of shoreline, 52 kilometers is the mainland shore and 5 kilometers is the shore of the islands.

• What fish are in Otter Lake?

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

• Is the water clear?

  All six monitoring sites with a phosphorus status are classified oligotrophic, the clearest of the province’s three bands.

• Is there a public boat launch?

  Records mark three boat launches, one shoreline access point, one marina and one beach on Otter Lake.