Mary Lake

Normal

Water level is right where you'd expect for mid-September and falling.

Low (8.51m)Normal rangeHigh (8.83m)

Current Weather

2d ago

19°CMainly Sunny

Wind N 9 km/h

Humidity 54%

A mix of sun and cloud

Environment Canada — Parry Sound - Muskoka

vs. Last Year

No data available

7-Day Trend

↓Falling

Down 6.8 cm over the past week

-6.8 cm over 7 days

Seasonal Position

66th percentile

Based on 22 years of records

Seasonal Outlook

Typical next 7 days

This lake usually drops moderately over the next week.

Typical next 14 days

Over two weeks, levels typically drops moderately.

Tracking

This year is moving slower than usual.

Based on 22 years of seasonal patterns. Moderate historical coverage. This is a historical seasonal pattern, not a forecast.

Fish Consumption Advisories (7 species)

The following consumption advisories are in effect for fish caught in Mary Lake.

⚠Lake Trout

Contaminant	Size	General pop.	Sensitive pop.
Mercury	30-35 cm	4/month	Do not eat
Mercury	35-40 cm	4/month	Do not eat
Mercury	25-30 cm	4/month	Do not eat
Mercury	40-45 cm	4/month	Do not eat
Mercury	45-50 cm	2/month	Do not eat
Mercury	50-55 cm	2/month	Do not eat
Mercury	55-60 cm	Do not eat	Do not eat
Mercury	60-65 cm	Do not eat	Do not eat
Mercury	65-70 cm	Do not eat	—
Mercury	70-75 cm	Do not eat	—
Mercury, PCB	>75 cm	Do not eat	Do not eat
Mercury, PCB	65-70 cm	—	Do not eat
Mercury, PCB	70-75 cm	—	Do not eat

⚠Northern Pike

Contaminant	Size	General pop.	Sensitive pop.
Mercury	65-70 cm	4/month	Do not eat
Mercury	60-65 cm	4/month	Do not eat

⚠Rainbow Smelt

Contaminant	Size	General pop.	Sensitive pop.
Mercury	20-25 cm	4/month	Do not eat
Mercury	15-20 cm	8/month	4/month

⚠Rock Bass

Contaminant	Size	General pop.	Sensitive pop.
Mercury	15-20 cm	4/month	Do not eat
Mercury	20-25 cm	Do not eat	Do not eat

⚠Smallmouth Bass

Contaminant	Size	General pop.	Sensitive pop.
Chromium	35-40 cm	2/month	Do not eat
Mercury	25-30 cm	8/month	4/month
Mercury	30-35 cm	4/month	Do not eat
Mercury	40-45 cm	2/month	Do not eat
Mercury	45-50 cm	Do not eat	Do not eat
Mercury	15-20 cm	16/month	4/month
Mercury	20-25 cm	8/month	4/month

⚠Walleye

Contaminant	Size	General pop.	Sensitive pop.
Mercury	55-60 cm	Do not eat	Do not eat
Mercury	45-50 cm	2/month	Do not eat
Mercury	50-55 cm	2/month	Do not eat
Mercury	25-30 cm	16/month	8/month
Mercury	30-35 cm	12/month	4/month
Mercury	35-40 cm	8/month	Do not eat
Mercury	40-45 cm	4/month	Do not eat

⚠Yellow Perch

Contaminant	Size	General pop.	Sensitive pop.
Mercury	20-25 cm	4/month	Do not eat

Source: Guide to Eating Ontario Fish (2025). Advisory data is updated annually.

Lake Profile

Est. average depth24.0 m

Estimated from HydroLAKES v1.0 (Messager et al., 2016). Modeled geo-statistical estimate, not a direct survey measurement.

Boat Launches (2)

Mary Lake - Port Sydney

0.5 kmMunicipalParking

Map ↗

Clearwater Lake

4.4 kmMunicipal

Map ↗

Source: Ontario MNR Fishing Access Points. Verify conditions before visiting.

Water Level — Last 30 Days

Technical details

Current level: 8.63 m
Reference value: 8.63 m (rolling_6h_mean)
Percentile for date: 66th percentile
Years of record: 22
Source station: MARY LAKE AT PORT SYDNEY (02EB021)
Est. average depth: 24.0 m
Relationship type: direct_lake
Mapping confidence: medium
Today's normal range: 8.59–8.64 m
Same-date historical range: 8.51–8.83 m
30-day change: -4.0 cm
Data confidence: medium
Observed at: Sep 20, 2026
Last snapshot: Sep 20, 2026

Data source: ECCC Water Office — Station 02EB021. Water level readings are provisional and subject to revision. This is not a navigation or flood-warning service.