Mermet Lake Water Temperature
Mermet Lake in Massac County, Illinois typically sits around 69°F at the surface in October — warmest in Jun (~83°F) and coldest in Apr (~62°F). That is a typical value for the month, not a live reading.
Typical water temperature by month
Typical surface water temperature by month, from 101 field readings (2016–2021) via the EPA Water Quality Portal. Months with too few readings are left blank.
Is Mermet Lake warm enough to swim?
Very comfortable for swimming. Warm surface water can also favor blue-green algae in nutrient-rich lakes, so check for advisories before you go in.
Want more than temperature? Mermet Lake scored F on water quality — clarity, algae, phosphorus, depth, fish species, and swimming safety, all on one report card.
Water temperatures at nearby Illinois lakes
Summer average ~77°F
Summer average ~75°F
Summer average ~73°F
Summer average ~82°F
Summer average ~78°F
Summer average ~80°F
Explore water temperatures
Where to stay near Mermet Lake
Planning a swim or lake trip? Compare cabins, lodges, and vacation rentals near Mermet Lake — live availability and prices. Switch the map to Satellite to see the lake and how close each stay is to the water.
Top-rated places to stay near Mermet Lake
Prices for Sep 4–6, 4 adults. Change dates on the map below.
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a trip to Mermet Lake?
Get lake water-quality report cards plus the best cabin & lodging deals near Mermet Lake — straight to your inbox. No spam, unsubscribe anytime.
Frequently asked questions
What is the water temperature of Mermet Lake?
Mermet Lake typically sits around 69°F at the surface in October, from 101 EPA Water Quality Portal field readings (2016–2021). That is a typical value for the month, not a live reading.
When is Mermet Lake warmest?
Surface water at Mermet Lake is typically warmest in June, reaching about 83°F. Lake surface temperature lags air temperature by several weeks, so the warmest water usually arrives in mid-to-late summer even though the hottest air can come earlier.
Is Mermet Lake warm enough to swim?
At its typical summer peak of about 83°F, Mermet Lake rates as "warm" for swimming. Very comfortable for swimming. Warm surface water can also favor blue-green algae in nutrient-rich lakes, so check for advisories before you go in.
Where does this Mermet Lake water temperature data come from?
Every temperature on this page is a typical (climatological) value computed from real surface-water field readings collected by state and federal agencies and published through the EPA Water Quality Portal — 101 readings from 3 monitoring stations between 2016 and 2021. They describe what is typical for each month, not the temperature right now.
About this data
Water temperatures are a climatology — the typical value for each month, averaged from real surface-water field readings collected by state and federal agencies and published through the EPA Water Quality Portal. They tell you what to expect, not the temperature at this moment. Actual conditions vary with recent weather, depth, and time of day.