Fon-du-Lac Reservoir Water Temperature
Fon-du-Lac Reservoir in Jefferson County, Missouri typically sits around 81°F at the surface in September — warmest in Jul (~87°F) and coldest in Apr (~64°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 23 field readings (2022–2024) via the EPA Water Quality Portal. Months with too few readings are left blank.
Is Fon-du-Lac Reservoir 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? Fon-du-Lac Reservoir scored F on water quality — clarity, algae, phosphorus, depth, fish species, and swimming safety, all on one report card.
Water temperatures at nearby Missouri lakes
Summer average ~84°F
Summer average ~84°F
Summer average ~83°F
Summer average ~84°F
Summer average ~85°F
Summer average ~84°F
Explore water temperatures
Where to stay near Fon-du-Lac Reservoir
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Top-rated places to stay near Fon-du-Lac Reservoir
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Frequently asked questions
What is the water temperature of Fon-du-Lac Reservoir?
Fon-du-Lac Reservoir typically sits around 81°F at the surface in September, from 23 EPA Water Quality Portal field readings (2022–2024). That is a typical value for the month, not a live reading.
When is Fon-du-Lac Reservoir warmest?
Surface water at Fon-du-Lac Reservoir is typically warmest in July, reaching about 87°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 Fon-du-Lac Reservoir warm enough to swim?
At its typical summer peak of about 85°F, Fon-du-Lac Reservoir 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 Fon-du-Lac Reservoir 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 — 23 readings from 1 monitoring station between 2022 and 2024. 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.