Mermet Lake Water Temperature
Mermet Lake in Massac County, Illinois averages about 83°F at the surface in summer — warmest in Jun (~83°F) and coldest in Apr (~62°F). These are typical values by 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 D 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
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Frequently asked questions
What is the water temperature of Mermet Lake?
Mermet Lake has a typical summer surface temperature of about 83°F. It is usually warmest in June (around 83°F) and coldest in April (around 62°F). These are typical values by month from 101 EPA Water Quality Portal field readings (2016–2021), 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.