Randolph Lake Water Temperature
Randolph Lake in Randolph County, Illinois averages about 71°F at the surface in summer — warmest in Jul (~73°F) and coldest in May (~61°F). These are typical values by month, not a live reading.
Typical water temperature by month
Typical surface water temperature by month, from 257 field readings (2016–2021) via the EPA Water Quality Portal. Months with too few readings are left blank.
Is Randolph Lake warm enough to swim?
Pleasant for swimming — the range most people find enjoyable without a wetsuit.
Want more than temperature? Randolph 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 ~69°F
Summer average ~84°F
Summer average ~67°F
Summer average ~68°F
Summer average ~61°F
Summer average ~86°F
Explore water temperatures
Where to stay near Randolph Lake
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Frequently asked questions
What is the water temperature of Randolph Lake?
Randolph Lake has a typical summer surface temperature of about 71°F. It is usually warmest in July (around 73°F) and coldest in May (around 61°F). These are typical values by month from 257 EPA Water Quality Portal field readings (2016–2021), not a live reading.
When is Randolph Lake warmest?
Surface water at Randolph Lake is typically warmest in July, reaching about 73°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 Randolph Lake warm enough to swim?
At its typical summer peak of about 71°F, Randolph Lake rates as "comfortable" for swimming. Pleasant for swimming — the range most people find enjoyable without a wetsuit.
Where does this Randolph 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 — 257 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.