Lake St Louis Water Temperature
Lake St Louis in St. Charles County, Missouri typically sits around 78°F at the surface in September — warmest in Jul (~86°F) and coldest in Apr (~62°F). That is a typical value for the month, not a live reading.
Typical water temperature by month
Column height runs from this lake’s coldest month (62°F) to its warmest (86°F).
Typical surface water temperature by month, from 33 field readings (2016–2020) via the EPA Water Quality Portal. Months with too few readings are left blank.
Is Lake St Louis 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? Lake St Louis water quality: clarity, algae, phosphorus, depth, fish species, and current advisories, all on one page.
Water temperatures at nearby Missouri lakes
Summer average ~82°F
Summer average ~83°F
Summer average ~82°F
Summer average ~81°F
Summer average ~84°F
Summer average ~81°F
Explore water temperatures
Where to stay near Lake St Louis
Planning a swim or lake trip? Compare cabins, lodges, and vacation rentals near Lake St Louis — 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 Lake St Louis
Prices for Oct 9–11, 4 adults. Change dates on the map below.
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Frequently asked questions
What is the water temperature of Lake St Louis?
Lake St Louis typically sits around 78°F at the surface in September, from 33 EPA Water Quality Portal field readings (2016–2020). That is a typical value for the month, not a live reading.
When is Lake St Louis warmest?
Surface water at Lake St Louis is typically warmest in July, reaching about 86°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 Lake St Louis warm enough to swim?
At its typical summer peak of about 82°F, Lake St Louis 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 Lake St Louis 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 — 33 readings from 2 monitoring stations between 2016 and 2020. 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.